Level 2

SorosLiu

Level 2

Solved 72 out of 622 problems

Completed 11% of the problems

Problems Solved

1
Problem 1 (solved by 736441 members)
Difficulty rating: 5%
Completed on Tue, 12 Dec 2017, 20:03
"Multiples of 3 and 5"
2
Problem 2 (solved by 592496 members)
Difficulty rating: 5%
Completed on Tue, 12 Dec 2017, 22:35
"Even Fibonacci numbers"
3
Problem 3 (solved by 424474 members)
Difficulty rating: 5%
Completed on Thu, 14 Dec 2017, 23:12
"Largest prime factor"
4
Problem 4 (solved by 378197 members)
Difficulty rating: 5%
Completed on Wed, 13 Dec 2017, 19:24
"Largest palindrome product"
5
Problem 5 (solved by 386833 members)
Difficulty rating: 5%
Completed on Thu, 14 Dec 2017, 23:04
"Smallest multiple"
6
Problem 6 (solved by 389095 members)
Difficulty rating: 5%
Completed on Fri, 15 Dec 2017, 00:19
"Sum square difference"
7
Problem 7 (solved by 333065 members)
Difficulty rating: 5%
Completed on Sat, 16 Dec 2017, 18:40
"10001st prime"
8
Problem 8 (solved by 281746 members)
Difficulty rating: 5%
Completed on Fri, 15 Dec 2017, 21:51
"Largest product in a series"
9
Problem 9 (solved by 284399 members)
Difficulty rating: 5%
Completed on Sat, 16 Dec 2017, 09:45
"Special Pythagorean triplet"
10
Problem 10 (solved by 260928 members)
Difficulty rating: 5%
Completed on Sat, 16 Dec 2017, 18:40
"Summation of primes"
11
Problem 11 (solved by 189443 members)
Difficulty rating: 5%
Completed on Mon, 18 Dec 2017, 21:20
"Largest product in a grid"
12
Problem 12 (solved by 176789 members)
Difficulty rating: 5%
Completed on Mon, 18 Dec 2017, 21:20
"Highly divisible triangular number"
13
Problem 13 (solved by 182551 members)
Difficulty rating: 5%
Completed on Sun, 24 Dec 2017, 14:50
"Large sum"
14
Problem 14 (solved by 181985 members)
Difficulty rating: 5%
Completed on Sun, 24 Dec 2017, 15:32
"Longest Collatz sequence"
15
Problem 15 (solved by 150501 members)
Difficulty rating: 5%
Completed on Sun, 24 Dec 2017, 22:51
"Lattice paths"
16
Problem 16 (solved by 184157 members)
Difficulty rating: 5%
Completed on Sun, 24 Dec 2017, 23:28
"Power digit sum"
17
Problem 17 (solved by 122620 members)
Difficulty rating: 5%
Completed on Mon, 25 Dec 2017, 00:18
"Number letter counts"
18
Problem 18 (solved by 117849 members)
Difficulty rating: 5%
Completed on Mon, 25 Dec 2017, 14:29
"Maximum path sum I"
19
Problem 19 (solved by 109541 members)
Difficulty rating: 5%
Completed on Mon, 25 Dec 2017, 18:24
"Counting Sundays"
20
Problem 20 (solved by 161649 members)
Difficulty rating: 5%
Completed on Tue, 26 Dec 2017, 00:07
"Factorial digit sum"
21
Problem 21 (solved by 118064 members)
Difficulty rating: 5%
Completed on Tue, 26 Dec 2017, 18:28
"Amicable numbers"
22
Problem 22 (solved by 109103 members)
Difficulty rating: 5%
Completed on Tue, 26 Dec 2017, 18:28
"Names scores"
23
Problem 23 (solved by 83837 members)
Difficulty rating: 5%
Completed on Tue, 26 Dec 2017, 18:28
"Non-abundant sums"
24
Problem 24 (solved by 93243 members)
Difficulty rating: 5%
Completed on Tue, 26 Dec 2017, 18:28
"Lexicographic permutations"
25
Problem 25 (solved by 126177 members)
Difficulty rating: 5%
Completed on Fri, 29 Dec 2017, 19:21
"1000-digit Fibonacci number"
26
Problem 26 (solved by 67639 members)
Difficulty rating: 5%
Completed on Fri, 29 Dec 2017, 19:21
"Reciprocal cycles"
27
Problem 27 (solved by 70760 members)
Difficulty rating: 5%
Completed on Fri, 29 Dec 2017, 19:21
"Quadratic primes"
28
Problem 28 (solved by 89133 members)
Difficulty rating: 5%
Completed on Fri, 29 Dec 2017, 19:21
"Number spiral diagonals"
29
Problem 29 (solved by 84985 members)
Difficulty rating: 5%
Completed on Fri, 29 Dec 2017, 19:21
"Distinct powers"
30
Problem 30 (solved by 89066 members)
Difficulty rating: 5%
Completed on Fri, 29 Dec 2017, 19:21
"Digit fifth powers"
31
Problem 31 (solved by 68042 members)
Difficulty rating: 5%
Completed on Tue, 02 Jan 2018, 20:32
"Coin sums"
32
Problem 32 (solved by 57463 members)
Difficulty rating: 5%
Completed on Tue, 02 Jan 2018, 20:32
"Pandigital products"
33
Problem 33 (solved by 58119 members)
Difficulty rating: 5%
Completed on Tue, 02 Jan 2018, 20:32
"Digit cancelling fractions"
34
Problem 34 (solved by 76576 members)
Difficulty rating: 5%
Completed on Wed, 03 Jan 2018, 20:19
"Digit factorials"
35
Problem 35 (solved by 69140 members)
Difficulty rating: 5%
Completed on Fri, 05 Jan 2018, 18:35
"Circular primes"
36
Problem 36 (solved by 72786 members)
Difficulty rating: 5%
Completed on Fri, 05 Jan 2018, 18:35
"Double-base palindromes"
37
Problem 37 (solved by 59712 members)
Difficulty rating: 5%
Completed on Fri, 05 Jan 2018, 18:35
"Truncatable primes"
38
Problem 38 (solved by 50884 members)
Difficulty rating: 5%
Completed on Fri, 05 Jan 2018, 18:35
"Pandigital multiples"
39
Problem 39 (solved by 59140 members)
Difficulty rating: 5%
Completed on Fri, 05 Jan 2018, 18:35
"Integer right triangles"
40
Problem 40 (solved by 65250 members)
Difficulty rating: 5%
Completed on Fri, 05 Jan 2018, 18:35
"Champernowne's constant"
41
Problem 41 (solved by 55056 members)
Difficulty rating: 5%
Completed on Sat, 06 Jan 2018, 13:39
"Pandigital prime"
42
Problem 42 (solved by 60936 members)
Difficulty rating: 5%
Completed on Sat, 06 Jan 2018, 13:58
"Coded triangle numbers"
43
Problem 43 (solved by 47982 members)
Difficulty rating: 5%
Completed on Sat, 06 Jan 2018, 15:15
"Sub-string divisibility"
44
Problem 44 (solved by 46611 members)
Difficulty rating: 5%
Completed on Sun, 07 Jan 2018, 11:21
"Pentagon numbers"
45
Problem 45 (solved by 57932 members)
Difficulty rating: 5%
Completed on Sun, 07 Jan 2018, 13:33
"Triangular, pentagonal, and hexagonal"
46
Problem 46 (solved by 49344 members)
Difficulty rating: 5%
Completed on Sun, 07 Jan 2018, 13:57
"Goldbach's other conjecture"
47
Problem 47 (solved by 46631 members)
Difficulty rating: 5%
Completed on Tue, 09 Jan 2018, 19:07
"Distinct primes factors"
48
Problem 48 (solved by 92956 members)
Difficulty rating: 5%
Completed on Tue, 09 Jan 2018, 19:07
"Self powers"
49
Problem 49 (solved by 46611 members)
Difficulty rating: 5%
Completed on Tue, 09 Jan 2018, 19:07
"Prime permutations"
50
Problem 50 (solved by 50218 members)
Difficulty rating: 5%
Completed on Tue, 09 Jan 2018, 19:07
"Consecutive prime sum"
51
Problem 51 (solved by 26299 members)
Difficulty rating: 15%
"Prime digit replacements"
52
Problem 52 (solved by 53230 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Permuted multiples"
53
Problem 53 (solved by 47962 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Combinatoric selections"
54
Problem 54 (solved by 28292 members)
Difficulty rating: 10%
Completed on Mon, 22 Jan 2018, 20:53
"Poker hands"
55
Problem 55 (solved by 43666 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Lychrel numbers"
56
Problem 56 (solved by 47330 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Powerful digit sum"
57
Problem 57 (solved by 33206 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Square root convergents"
58
Problem 58 (solved by 32170 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Spiral primes"
59
Problem 59 (solved by 33729 members)
Difficulty rating: 5%
Completed on Wed, 24 Jan 2018, 19:02
"XOR decryption"
60
Problem 60 (solved by 20627 members)
Difficulty rating: 20%
"Prime pair sets"
61
Problem 61 (solved by 20081 members)
Difficulty rating: 20%
"Cyclical figurate numbers"
62
Problem 62 (solved by 24775 members)
Difficulty rating: 15%
Completed on Mon, 29 Jan 2018, 21:36
"Cubic permutations"
63
Problem 63 (solved by 34712 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Powerful digit counts"
64
Problem 64 (solved by 17493 members)
Difficulty rating: 20%
"Odd period square roots"
65
Problem 65 (solved by 24084 members)
Difficulty rating: 15%
"Convergents of e"
66
Problem 66 (solved by 15529 members)
Difficulty rating: 25%
"Diophantine equation"
67
Problem 67 (solved by 79598 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Maximum path sum II"
68
Problem 68 (solved by 16413 members)
Difficulty rating: 25%
"Magic 5-gon ring"
69
Problem 69 (solved by 27330 members)
Difficulty rating: 10%
Completed on Wed, 24 Jan 2018, 19:01
"Totient maximum"
70
Problem 70 (solved by 17730 members)
Difficulty rating: 20%
"Totient permutation"
71
Problem 71 (solved by 23173 members)
Difficulty rating: 10%
Completed on Wed, 24 Jan 2018, 21:32
"Ordered fractions"
72
Problem 72 (solved by 17708 members)
Difficulty rating: 20%
"Counting fractions"
73
Problem 73 (solved by 20181 members)
Difficulty rating: 15%
"Counting fractions in a range"
74
Problem 74 (solved by 21301 members)
Difficulty rating: 15%
"Digit factorial chains"
75
Problem 75 (solved by 14154 members)
Difficulty rating: 25%
"Singular integer right triangles"
76
Problem 76 (solved by 22891 members)
Difficulty rating: 10%
Completed on Fri, 26 Jan 2018, 20:41
"Counting summations"
77
Problem 77 (solved by 15068 members)
Difficulty rating: 25%
"Prime summations"
78
Problem 78 (solved by 13258 members)
Difficulty rating: 30%
"Coin partitions"
79
Problem 79 (solved by 34618 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Passcode derivation"
80
Problem 80 (solved by 15842 members)
Difficulty rating: 20%
"Square root digital expansion"
81
Problem 81 (solved by 27931 members)
Difficulty rating: 10%
Completed on Thu, 25 Jan 2018, 20:57
"Path sum: two ways"
82
Problem 82 (solved by 16939 members)
Difficulty rating: 20%
Completed on Thu, 25 Jan 2018, 20:57
"Path sum: three ways"
83
Problem 83 (solved by 14499 members)
Difficulty rating: 25%
Completed on Sun, 28 Jan 2018, 20:58
"Path sum: four ways"
84
Problem 84 (solved by 9869 members)
Difficulty rating: 35%
"Monopoly odds"
85
Problem 85 (solved by 19858 members)
Difficulty rating: 15%
"Counting rectangles"
86
Problem 86 (solved by 10020 members)
Difficulty rating: 35%
"Cuboid route"
87
Problem 87 (solved by 16650 members)
Difficulty rating: 20%
"Prime power triples"
88
Problem 88 (solved by 7729 members)
Difficulty rating: 40%
"Product-sum numbers"
89
Problem 89 (solved by 17466 members)
Difficulty rating: 20%
"Roman numerals"
90
Problem 90 (solved by 8699 members)
Difficulty rating: 40%
"Cube digit pairs"
91
Problem 91 (solved by 12266 members)
Difficulty rating: 25%
"Right triangles with integer coordinates"
92
Problem 92 (solved by 34108 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Square digit chains"
93
Problem 93 (solved by 9170 members)
Difficulty rating: 35%
"Arithmetic expressions"
94
Problem 94 (solved by 9584 members)
Difficulty rating: 35%
"Almost equilateral triangles"
95
Problem 95 (solved by 11179 members)
Difficulty rating: 30%
"Amicable chains"
96
Problem 96 (solved by 13442 members)
Difficulty rating: 25%
"Su Doku"
97
Problem 97 (solved by 36414 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Large non-Mersenne prime"
98
Problem 98 (solved by 8857 members)
Difficulty rating: 35%
"Anagramic squares"
99
Problem 99 (solved by 24685 members)
Difficulty rating: 10%
Completed on Wed, 07 Feb 2018, 23:35
"Largest exponential"
100
Problem 100 (solved by 12776 members)
Difficulty rating: 30%
"Arranged probability"
101
Problem 101 (solved by 8797 members)
Difficulty rating: 35%
"Optimum polynomial"
102
Problem 102 (solved by 17468 members)
Difficulty rating: 15%
"Triangle containment"
103
Problem 103 (solved by 6222 members)
Difficulty rating: 45%
"Special subset sums: optimum"
104
Problem 104 (solved by 13091 members)
Difficulty rating: 25%
"Pandigital Fibonacci ends"
105
Problem 105 (solved by 6248 members)
Difficulty rating: 45%
"Special subset sums: testing"
106
Problem 106 (solved by 4981 members)
Difficulty rating: 50%
"Special subset sums: meta-testing"
107
Problem 107 (solved by 8811 members)
Difficulty rating: 35%
"Minimal network"
108
Problem 108 (solved by 10256 members)
Difficulty rating: 30%
"Diophantine reciprocals I"
109
Problem 109 (solved by 6363 members)
Difficulty rating: 45%
"Darts"
110
Problem 110 (solved by 6463 members)
Difficulty rating: 40%
"Diophantine reciprocals II"
111
Problem 111 (solved by 5661 members)
Difficulty rating: 45%
"Primes with runs"
112
Problem 112 (solved by 19765 members)
Difficulty rating: 15%
"Bouncy numbers"
113
Problem 113 (solved by 8913 members)
Difficulty rating: 30%
"Non-bouncy numbers"
114
Problem 114 (solved by 8617 members)
Difficulty rating: 35%
"Counting block combinations I"
115
Problem 115 (solved by 7881 members)
Difficulty rating: 35%
"Counting block combinations II"
116
Problem 116 (solved by 9639 members)
Difficulty rating: 30%
"Red, green or blue tiles"
117
Problem 117 (solved by 8841 members)
Difficulty rating: 35%
"Red, green, and blue tiles"
118
Problem 118 (solved by 5376 members)
Difficulty rating: 45%
"Pandigital prime sets"
119
Problem 119 (solved by 9822 members)
Difficulty rating: 30%
"Digit power sum"
120
Problem 120 (solved by 11193 members)
Difficulty rating: 25%
"Square remainders"
121
Problem 121 (solved by 7745 members)
Difficulty rating: 35%
"Disc game prize fund"
122
Problem 122 (solved by 6083 members)
Difficulty rating: 40%
"Efficient exponentiation"
123
Problem 123 (solved by 9282 members)
Difficulty rating: 30%
"Prime square remainders"
124
Problem 124 (solved by 11226 members)
Difficulty rating: 25%
"Ordered radicals"
125
Problem 125 (solved by 10948 members)
Difficulty rating: 25%
"Palindromic sums"
126
Problem 126 (solved by 3633 members)
Difficulty rating: 55%
"Cuboid layers"
127
Problem 127 (solved by 4841 members)
Difficulty rating: 50%
"abc-hits"
128
Problem 128 (solved by 3869 members)
Difficulty rating: 55%
"Hexagonal tile differences"
129
Problem 129 (solved by 4966 members)
Difficulty rating: 45%
"Repunit divisibility"
130
Problem 130 (solved by 4680 members)
Difficulty rating: 45%
"Composites with prime repunit property"
131
Problem 131 (solved by 5868 members)
Difficulty rating: 40%
"Prime cube partnership"
132
Problem 132 (solved by 5018 members)
Difficulty rating: 45%
"Large repunit factors"
133
Problem 133 (solved by 4344 members)
Difficulty rating: 50%
"Repunit nonfactors"
134
Problem 134 (solved by 5511 members)
Difficulty rating: 45%
"Prime pair connection"
135
Problem 135 (solved by 5018 members)
Difficulty rating: 45%
"Same differences"
136
Problem 136 (solved by 4405 members)
Difficulty rating: 50%
"Singleton difference"
137
Problem 137 (solved by 4278 members)
Difficulty rating: 50%
"Fibonacci golden nuggets"
138
Problem 138 (solved by 4556 members)
Difficulty rating: 45%
"Special isosceles triangles"
139
Problem 139 (solved by 4403 members)
Difficulty rating: 50%
"Pythagorean tiles"
140
Problem 140 (solved by 3332 members)
Difficulty rating: 55%
"Modified Fibonacci golden nuggets"
141
Problem 141 (solved by 2961 members)
Difficulty rating: 60%
", which are also square"
142
Problem 142 (solved by 4610 members)
Difficulty rating: 45%
"Perfect Square Collection"
143
Problem 143 (solved by 2040 members)
Difficulty rating: 65%
"Investigating the Torricelli point of a triangle"
144
Problem 144 (solved by 4863 members)
Difficulty rating: 50%
"Investigating multiple reflections of a laser beam"
145
Problem 145 (solved by 13336 members)
Difficulty rating: 20%
"How many reversible numbers are there below one-billion?"
146
Problem 146 (solved by 3942 members)
Difficulty rating: 50%
"Investigating a Prime Pattern "
147
Problem 147 (solved by 2308 members)
Difficulty rating: 65%
"Rectangles in cross-hatched grids"
148
Problem 148 (solved by 4053 members)
Difficulty rating: 50%
"Exploring Pascal's triangle"
149
Problem 149 (solved by 3827 members)
Difficulty rating: 50%
"Searching for a maximum-sum subsequence"
150
Problem 150 (solved by 3130 members)
Difficulty rating: 55%
"Searching a triangular array for a sub-triangle having minimum-sum"
151
Problem 151 (solved by 4313 members)
Difficulty rating: 50%
"Paper sheets of standard sizes: an expected-value problem"
152
Problem 152 (solved by 2008 members)
Difficulty rating: 65%
"Writing 1/2 as a sum of inverse squares"
153
Problem 153 (solved by 1985 members)
Difficulty rating: 65%
"Investigating Gaussian Integers"
154
Problem 154 (solved by 2026 members)
Difficulty rating: 65%
"Exploring Pascal's pyramid"
155
Problem 155 (solved by 2784 members)
Difficulty rating: 60%
"Counting Capacitor Circuits"
156
Problem 156 (solved by 1818 members)
Difficulty rating: 70%
"Counting Digits"
157
Problem 157 (solved by 2067 members)
Difficulty rating: 65%
""
158
Problem 158 (solved by 2846 members)
Difficulty rating: 55%
"Exploring strings for which only one character comes lexicographically after its neighbour to the left"
159
Problem 159 (solved by 2566 members)
Difficulty rating: 60%
"Digital root sums of factorisations"
160
Problem 160 (solved by 2688 members)
Difficulty rating: 60%
"Factorial trailing digits"
161
Problem 161 (solved by 1592 members)
Difficulty rating: 70%
"Triominoes"
162
Problem 162 (solved by 4342 members)
Difficulty rating: 45%
"Hexadecimal numbers"
163
Problem 163 (solved by 1404 members)
Difficulty rating: 70%
"Cross-hatched triangles"
164
Problem 164 (solved by 4559 members)
Difficulty rating: 45%
"Numbers for which no three consecutive digits have a sum greater than a given value"
165
Problem 165 (solved by 1990 members)
Difficulty rating: 65%
"Intersections"
166
Problem 166 (solved by 3200 members)
Difficulty rating: 50%
"Criss Cross"
167
Problem 167 (solved by 1303 members)
Difficulty rating: 75%
"Investigating Ulam sequences"
168
Problem 168 (solved by 2058 members)
Difficulty rating: 65%
"Number Rotations"
169
Problem 169 (solved by 4003 members)
Difficulty rating: 50%
"Exploring the number of different ways a number can be expressed as a sum of powers of 2"
170
Problem 170 (solved by 1506 members)
Difficulty rating: 70%
"Find the largest 0 to 9 pandigital that can be formed by concatenating products"
171
Problem 171 (solved by 2126 members)
Difficulty rating: 65%
"Finding numbers for which the sum of the squares of the digits is a square"
172
Problem 172 (solved by 2989 members)
Difficulty rating: 55%
"Investigating numbers with few repeated digits"
173
Problem 173 (solved by 7446 members)
Difficulty rating: 30%
"Using up to one million tiles how many different "hollow" square laminae can be formed?"
174
Problem 174 (solved by 4779 members)
Difficulty rating: 40%
"Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements"
175
Problem 175 (solved by 1375 members)
Difficulty rating: 70%
"Fractions involving the number of different ways a number can be expressed as a sum of powers of 2"
176
Problem 176 (solved by 1481 members)
Difficulty rating: 70%
"Right-angled triangles that share a cathetus"
177
Problem 177 (solved by 948 members)
Difficulty rating: 80%
"Integer angled Quadrilaterals"
178
Problem 178 (solved by 2653 members)
Difficulty rating: 55%
"Step Numbers"
179
Problem 179 (solved by 9236 members)
Difficulty rating: 25%
"Consecutive positive divisors"
180
Problem 180 (solved by 1196 members)
Difficulty rating: 75%
"Rational zeros of a function of three variables"
181
Problem 181 (solved by 1549 members)
Difficulty rating: 70%
"Investigating in how many ways objects of two different colours can be grouped"
182
Problem 182 (solved by 2036 members)
Difficulty rating: 60%
"RSA encryption"
183
Problem 183 (solved by 3784 members)
Difficulty rating: 45%
"Maximum product of parts"
184
Problem 184 (solved by 1230 members)
Difficulty rating: 75%
"Triangles containing the origin"
185
Problem 185 (solved by 2437 members)
Difficulty rating: 55%
"Number Mind"
186
Problem 186 (solved by 2238 members)
Difficulty rating: 60%
"Connectedness of a network"
187
Problem 187 (solved by 9187 members)
Difficulty rating: 25%
"Semiprimes"
188
Problem 188 (solved by 5238 members)
Difficulty rating: 35%
"The hyperexponentiation of a number"
189
Problem 189 (solved by 1601 members)
Difficulty rating: 70%
"Tri-colouring a triangular grid"
190
Problem 190 (solved by 3342 members)
Difficulty rating: 50%
"Maximising a weighted product"
191
Problem 191 (solved by 5770 members)
Difficulty rating: 35%
"Prize Strings"
192
Problem 192 (solved by 1213 members)
Difficulty rating: 75%
"Best Approximations"
193
Problem 193 (solved by 2560 members)
Difficulty rating: 55%
"Squarefree Numbers"
194
Problem 194 (solved by 1064 members)
Difficulty rating: 75%
"Coloured Configurations"
195
Problem 195 (solved by 1022 members)
Difficulty rating: 75%
"Inscribed circles of triangles with one angle of 60 degrees"
196
Problem 196 (solved by 1976 members)
Difficulty rating: 65%
"Prime triplets"
197
Problem 197 (solved by 4049 members)
Difficulty rating: 45%
"Investigating the behaviour of a recursively defined sequence"
198
Problem 198 (solved by 837 members)
Difficulty rating: 80%
"Ambiguous Numbers"
199
Problem 199 (solved by 1476 members)
Difficulty rating: 70%
"Iterative Circle Packing"
200
Problem 200 (solved by 1808 members)
Difficulty rating: 65%
"Find the 200th prime-proof sqube containing the contiguous sub-string "200"
201
Problem 201 (solved by 1782 members)
Difficulty rating: 65%
"Subsets with a unique sum"
202
Problem 202 (solved by 1943 members)
Difficulty rating: 60%
"Laserbeam"
203
Problem 203 (solved by 7439 members)
Difficulty rating: 25%
"Squarefree Binomial Coefficients"
204
Problem 204 (solved by 5990 members)
Difficulty rating: 30%
"Generalised Hamming Numbers"
205
Problem 205 (solved by 12005 members)
Difficulty rating: 15%
"Dice Game"
206
Problem 206 (solved by 19156 members)
Difficulty rating: 5%
Completed on Tue, 30 Jan 2018, 18:56
"Concealed Square"
207
Problem 207 (solved by 3852 members)
Difficulty rating: 40%
"Integer partition equations"
208
Problem 208 (solved by 1369 members)
Difficulty rating: 70%
"Robot Walks"
209
Problem 209 (solved by 2000 members)
Difficulty rating: 60%
"Circular Logic"
210
Problem 210 (solved by 1341 members)
Difficulty rating: 70%
"Obtuse Angled Triangles"
211
Problem 211 (solved by 3317 members)
Difficulty rating: 50%
"Divisor Square Sum"
212
Problem 212 (solved by 1072 members)
Difficulty rating: 70%
"Combined Volume of Cuboids"
213
Problem 213 (solved by 1832 members)
Difficulty rating: 60%
"Flea Circus"
214
Problem 214 (solved by 4252 members)
Difficulty rating: 40%
"Totient Chains"
215
Problem 215 (solved by 2982 members)
Difficulty rating: 50%
"Crack-free Walls"
216
Problem 216 (solved by 3228 members)
Difficulty rating: 45%
"-1"
217
Problem 217 (solved by 1161 members)
Difficulty rating: 70%
"Balanced Numbers"
218
Problem 218 (solved by 2425 members)
Difficulty rating: 55%
"Perfect right-angled triangles"
219
Problem 219 (solved by 1187 members)
Difficulty rating: 70%
"Skew-cost coding"
220
Problem 220 (solved by 1814 members)
Difficulty rating: 55%
"Heighway Dragon"
221
Problem 221 (solved by 1631 members)
Difficulty rating: 65%
"Alexandrian Integers"
222
Problem 222 (solved by 1651 members)
Difficulty rating: 60%
"Sphere Packing"
223
Problem 223 (solved by 1160 members)
Difficulty rating: 70%
"Almost right-angled triangles I"
224
Problem 224 (solved by 931 members)
Difficulty rating: 75%
"Almost right-angled triangles II"
225
Problem 225 (solved by 3647 members)
Difficulty rating: 45%
"Tribonacci non-divisors"
226
Problem 226 (solved by 1412 members)
Difficulty rating: 65%
"A Scoop of Blancmange"
227
Problem 227 (solved by 1647 members)
Difficulty rating: 65%
"The Chase"
228
Problem 228 (solved by 1044 members)
Difficulty rating: 70%
"Minkowski Sums"
229
Problem 229 (solved by 1173 members)
Difficulty rating: 70%
"Four Representations using Squares"
230
Problem 230 (solved by 2360 members)
Difficulty rating: 50%
"Fibonacci Words"
231
Problem 231 (solved by 4442 members)
Difficulty rating: 40%
"The prime factorisation of binomial coefficients"
232
Problem 232 (solved by 1377 members)
Difficulty rating: 65%
"The Race"
233
Problem 233 (solved by 1730 members)
Difficulty rating: 70%
"Lattice points on a circle"
234
Problem 234 (solved by 2697 members)
Difficulty rating: 50%
"Semidivisible numbers"
235
Problem 235 (solved by 4164 members)
Difficulty rating: 40%
"An Arithmetic Geometric sequence"
236
Problem 236 (solved by 730 members)
Difficulty rating: 80%
"Luxury Hampers"
237
Problem 237 (solved by 1212 members)
Difficulty rating: 70%
"Tours on a 4 x n playing board"
238
Problem 238 (solved by 758 members)
Difficulty rating: 75%
"Infinite string tour"
239
Problem 239 (solved by 1425 members)
Difficulty rating: 65%
"Twenty-two Foolish Primes"
240
Problem 240 (solved by 1753 members)
Difficulty rating: 60%
"Top Dice"
241
Problem 241 (solved by 704 members)
Difficulty rating: 80%
"Perfection Quotients"
242
Problem 242 (solved by 819 members)
Difficulty rating: 75%
"Odd Triplets"
243
Problem 243 (solved by 7742 members)
Difficulty rating: 35%
"Resilience"
244
Problem 244 (solved by 1031 members)
Difficulty rating: 70%
"Sliders"
245
Problem 245 (solved by 651 members)
Difficulty rating: 80%
"Coresilience"
246
Problem 246 (solved by 620 members)
Difficulty rating: 80%
"Tangents to an ellipse"
247
Problem 247 (solved by 1162 members)
Difficulty rating: 65%
"Squares under a hyperbola"
248
Problem 248 (solved by 1012 members)
Difficulty rating: 70%
"Numbers for which Euler’s totient function equals 13!"
249
Problem 249 (solved by 2039 members)
Difficulty rating: 60%
"Prime Subset Sums"
250
Problem 250 (solved by 2366 members)
Difficulty rating: 55%
"250250"
251
Problem 251 (solved by 1041 members)
Difficulty rating: 70%
"Cardano Triplets"
252
Problem 252 (solved by 655 members)
Difficulty rating: 80%
"Convex Holes"
253
Problem 253 (solved by 793 members)
Difficulty rating: 75%
"Tidying up"
254
Problem 254 (solved by 739 members)
Difficulty rating: 75%
"Sums of Digit Factorials"
255
Problem 255 (solved by 703 members)
Difficulty rating: 75%
"Rounded Square Roots"
256
Problem 256 (solved by 574 members)
Difficulty rating: 80%
"Tatami-Free Rooms"
257
Problem 257 (solved by 520 members)
Difficulty rating: 85%
"Angular Bisectors"
258
Problem 258 (solved by 1187 members)
Difficulty rating: 70%
"A lagged Fibonacci sequence"
259
Problem 259 (solved by 1222 members)
Difficulty rating: 70%
"Reachable Numbers"
260
Problem 260 (solved by 1018 members)
Difficulty rating: 70%
"Stone Game"
261
Problem 261 (solved by 518 members)
Difficulty rating: 85%
"Pivotal Square Sums"
262
Problem 262 (solved by 560 members)
Difficulty rating: 80%
"Mountain Range"
263
Problem 263 (solved by 826 members)
Difficulty rating: 75%
"An engineers' dream come true"
264
Problem 264 (solved by 452 members)
Difficulty rating: 85%
"Triangle Centres"
265
Problem 265 (solved by 3407 members)
Difficulty rating: 40%
"Binary Circles"
266
Problem 266 (solved by 1337 members)
Difficulty rating: 65%
"Pseudo Square Root"
267
Problem 267 (solved by 2705 members)
Difficulty rating: 50%
"Billionaire"
268
Problem 268 (solved by 1127 members)
Difficulty rating: 70%
"Counting numbers with at least four distinct prime factors less than 100"
269
Problem 269 (solved by 533 members)
Difficulty rating: 80%
"Polynomials with at least one integer root"
270
Problem 270 (solved by 515 members)
Difficulty rating: 80%
"Cutting Squares"
271
Problem 271 (solved by 1851 members)
Difficulty rating: 60%
"Modular Cubes, part 1"
272
Problem 272 (solved by 719 members)
Difficulty rating: 80%
"Modular Cubes, part 2"
273
Problem 273 (solved by 1058 members)
Difficulty rating: 70%
"Sum of Squares"
274
Problem 274 (solved by 1147 members)
Difficulty rating: 65%
"Divisibility Multipliers"
275
Problem 275 (solved by 473 members)
Difficulty rating: 85%
"Balanced Sculptures"
276
Problem 276 (solved by 839 members)
Difficulty rating: 75%
"Primitive Triangles"
277
Problem 277 (solved by 2540 members)
Difficulty rating: 35%
"A Modified Collatz sequence"
278
Problem 278 (solved by 789 members)
Difficulty rating: 50%
"Linear Combinations of Semiprimes"
279
Problem 279 (solved by 540 members)
Difficulty rating: 60%
"Triangles with integral sides and an integral angle "
280
Problem 280 (solved by 810 members)
Difficulty rating: 65%
"Ant and seeds"
281
Problem 281 (solved by 712 members)
Difficulty rating: 55%
"Pizza Toppings"
282
Problem 282 (solved by 755 members)
Difficulty rating: 70%
"The Ackermann function"
283
Problem 283 (solved by 520 members)
Difficulty rating: 75%
"Integer sided triangles for which the area/perimeter ratio is integral"
284
Problem 284 (solved by 991 members)
Difficulty rating: 55%
"Steady Squares"
285
Problem 285 (solved by 919 members)
Difficulty rating: 55%
"Pythagorean odds"
286
Problem 286 (solved by 1671 members)
Difficulty rating: 50%
"Scoring probabilities"
287
Problem 287 (solved by 1113 members)
Difficulty rating: 40%
"Quadtree encoding (a simple compression algorithm)"
288
Problem 288 (solved by 1258 members)
Difficulty rating: 35%
"An enormous factorial"
289
Problem 289 (solved by 382 members)
Difficulty rating: 90%
"Eulerian Cycles"
290
Problem 290 (solved by 775 members)
Difficulty rating: 50%
"Digital Signature"
291
Problem 291 (solved by 1090 members)
Difficulty rating: 45%
"Panaitopol Primes"
292
Problem 292 (solved by 464 members)
Difficulty rating: 65%
"Pythagorean Polygons"
293
Problem 293 (solved by 2269 members)
Difficulty rating: 30%
"Pseudo-Fortunate Numbers"
294
Problem 294 (solved by 695 members)
Difficulty rating: 45%
"Sum of digits - experience #23"
295
Problem 295 (solved by 375 members)
Difficulty rating: 75%
"Lenticular holes"
296
Problem 296 (solved by 455 members)
Difficulty rating: 60%
"Angular Bisector and Tangent"
297
Problem 297 (solved by 2249 members)
Difficulty rating: 35%
"Zeckendorf Representation"
298
Problem 298 (solved by 529 members)
Difficulty rating: 60%
"Selective Amnesia"
299
Problem 299 (solved by 493 members)
Difficulty rating: 60%
"Three similar triangles"
300
Problem 300 (solved by 847 members)
Difficulty rating: 50%
"Protein folding"
301
Problem 301 (solved by 4769 members)
Difficulty rating: 15%
"Nim"
302
Problem 302 (solved by 580 members)
Difficulty rating: 60%
"Strong Achilles Numbers"
303
Problem 303 (solved by 2839 members)
Difficulty rating: 35%
"Multiples with small digits"
304
Problem 304 (solved by 1670 members)
Difficulty rating: 35%
"Primonacci"
305
Problem 305 (solved by 495 members)
Difficulty rating: 60%
"Reflexive Position"
306
Problem 306 (solved by 855 members)
Difficulty rating: 55%
"Paper-strip Game"
307
Problem 307 (solved by 1250 members)
Difficulty rating: 35%
"Chip Defects"
308
Problem 308 (solved by 605 members)
Difficulty rating: 60%
"An amazing Prime-generating Automaton"
309
Problem 309 (solved by 605 members)
Difficulty rating: 50%
"Integer Ladders"
310
Problem 310 (solved by 813 members)
Difficulty rating: 40%
"Nim Square"
311
Problem 311 (solved by 353 members)
Difficulty rating: 70%
"Biclinic Integral Quadrilaterals"
312
Problem 312 (solved by 650 members)
Difficulty rating: 50%
"Cyclic paths on Sierpiński graphs"
313
Problem 313 (solved by 1203 members)
Difficulty rating: 30%
"Sliding game"
314
Problem 314 (solved by 398 members)
Difficulty rating: 80%
"The Mouse on the Moon"
315
Problem 315 (solved by 2469 members)
Difficulty rating: 20%
"Digital root clocks"
316
Problem 316 (solved by 501 members)
Difficulty rating: 55%
"Numbers in decimal expansions"
317
Problem 317 (solved by 1950 members)
Difficulty rating: 35%
"Firecracker"
318
Problem 318 (solved by 687 members)
Difficulty rating: 50%
"2011 nines"
319
Problem 319 (solved by 313 members)
Difficulty rating: 90%
"Bounded Sequences"
320
Problem 320 (solved by 664 members)
Difficulty rating: 50%
"Factorials divisible by a huge integer"
321
Problem 321 (solved by 1312 members)
Difficulty rating: 30%
"Swapping Counters"
322
Problem 322 (solved by 359 members)
Difficulty rating: 70%
"Binomial coefficients divisible by 10"
323
Problem 323 (solved by 2910 members)
Difficulty rating: 20%
"Bitwise-OR operations on random integers"
324
Problem 324 (solved by 519 members)
Difficulty rating: 50%
"Building a tower"
325
Problem 325 (solved by 443 members)
Difficulty rating: 80%
"Stone Game II"
326
Problem 326 (solved by 401 members)
Difficulty rating: 55%
"Modulo Summations"
327
Problem 327 (solved by 884 members)
Difficulty rating: 40%
"Rooms of Doom"
328
Problem 328 (solved by 305 members)
Difficulty rating: 95%
"Lowest-cost Search"
329
Problem 329 (solved by 1884 members)
Difficulty rating: 25%
"Prime Frog"
330
Problem 330 (solved by 395 members)
Difficulty rating: 70%
"Euler's Number"
331
Problem 331 (solved by 283 members)
Difficulty rating: 100%
"Cross flips"
332
Problem 332 (solved by 457 members)
Difficulty rating: 50%
"Spherical triangles"
333
Problem 333 (solved by 915 members)
Difficulty rating: 35%
"Special partitions"
334
Problem 334 (solved by 363 members)
Difficulty rating: 65%
"Spilling the beans"
335
Problem 335 (solved by 391 members)
Difficulty rating: 65%
"Gathering the beans"
336
Problem 336 (solved by 1585 members)
Difficulty rating: 25%
"Maximix Arrangements"
337
Problem 337 (solved by 385 members)
Difficulty rating: 70%
"Totient Stairstep Sequences"
338
Problem 338 (solved by 259 members)
Difficulty rating: 95%
"Cutting Rectangular Grid Paper"
339
Problem 339 (solved by 425 members)
Difficulty rating: 70%
"Peredur fab Efrawg"
340
Problem 340 (solved by 817 members)
Difficulty rating: 30%
"Crazy Function"
341
Problem 341 (solved by 711 members)
Difficulty rating: 45%
"Golomb's self-describing sequence"
342
Problem 342 (solved by 633 members)
Difficulty rating: 50%
"The totient of a square is a cube"
343
Problem 343 (solved by 1088 members)
Difficulty rating: 35%
"Fractional Sequences"
344
Problem 344 (solved by 239 members)
Difficulty rating: 100%
"Silver dollar game"
345
Problem 345 (solved by 3972 members)
Difficulty rating: 15%
"Matrix Sum"
346
Problem 346 (solved by 2932 members)
Difficulty rating: 15%
"Strong Repunits"
347
Problem 347 (solved by 3146 members)
Difficulty rating: 15%
"Largest integer divisible by two primes"
348
Problem 348 (solved by 2222 members)
Difficulty rating: 25%
"Sum of a square and a cube"
349
Problem 349 (solved by 1456 members)
Difficulty rating: 35%
"Langton's ant"
350
Problem 350 (solved by 367 members)
Difficulty rating: 60%
"Constraining the least greatest and the greatest least"
351
Problem 351 (solved by 1917 members)
Difficulty rating: 25%
"Hexagonal orchards"
352
Problem 352 (solved by 461 members)
Difficulty rating: 55%
"Blood tests"
353
Problem 353 (solved by 367 members)
Difficulty rating: 50%
"Risky moon"
354
Problem 354 (solved by 328 members)
Difficulty rating: 65%
"Distances in a bee's honeycomb "
355
Problem 355 (solved by 398 members)
Difficulty rating: 70%
"Maximal coprime subset"
356
Problem 356 (solved by 418 members)
Difficulty rating: 60%
"Largest roots of cubic polynomials"
357
Problem 357 (solved by 5683 members)
Difficulty rating: 10%
"Prime generating integers"
358
Problem 358 (solved by 1240 members)
Difficulty rating: 25%
"Cyclic numbers"
359
Problem 359 (solved by 1157 members)
Difficulty rating: 25%
"Hilbert's New Hotel"
360
Problem 360 (solved by 477 members)
Difficulty rating: 50%
"Scary Sphere"
361
Problem 361 (solved by 240 members)
Difficulty rating: 90%
"Subsequence of Thue-Morse sequence"
362
Problem 362 (solved by 358 members)
Difficulty rating: 70%
"Squarefree factors"
363
Problem 363 (solved by 810 members)
Difficulty rating: 35%
"Bézier Curves"
364
Problem 364 (solved by 523 members)
Difficulty rating: 50%
"Comfortable distance"
365
Problem 365 (solved by 905 members)
Difficulty rating: 40%
"A huge binomial coefficient"
366
Problem 366 (solved by 464 members)
Difficulty rating: 40%
"Stone Game III"
367
Problem 367 (solved by 374 members)
Difficulty rating: 55%
"Bozo sort"
368
Problem 368 (solved by 436 members)
Difficulty rating: 45%
"A Kempner-like series"
369
Problem 369 (solved by 367 members)
Difficulty rating: 60%
"Badugi"
370
Problem 370 (solved by 404 members)
Difficulty rating: 65%
"Geometric triangles"
371
Problem 371 (solved by 1212 members)
Difficulty rating: 30%
"Licence plates"
372
Problem 372 (solved by 319 members)
Difficulty rating: 60%
"Pencils of rays"
373
Problem 373 (solved by 272 members)
Difficulty rating: 75%
"Circumscribed Circles"
374
Problem 374 (solved by 511 members)
Difficulty rating: 40%
"Maximum Integer Partition Product"
375
Problem 375 (solved by 655 members)
Difficulty rating: 40%
"Minimum of subsequences"
376
Problem 376 (solved by 212 members)
Difficulty rating: 70%
"Nontransitive sets of dice"
377
Problem 377 (solved by 523 members)
Difficulty rating: 45%
"Sum of digits, experience 13"
378
Problem 378 (solved by 608 members)
Difficulty rating: 35%
"Triangle Triples"
379
Problem 379 (solved by 383 members)
Difficulty rating: 70%
"Least common multiple count"
380
Problem 380 (solved by 393 members)
Difficulty rating: 60%
"Amazing Mazes!"
381
Problem 381 (solved by 3030 members)
Difficulty rating: 15%
"(prime-k) factorial"
382
Problem 382 (solved by 265 members)
Difficulty rating: 60%
"Generating polygons"
383
Problem 383 (solved by 388 members)
Difficulty rating: 50%
"Divisibility comparison between factorials"
384
Problem 384 (solved by 267 members)
Difficulty rating: 65%
"Rudin-Shapiro sequence"
385
Problem 385 (solved by 224 members)
Difficulty rating: 70%
"Ellipses inside triangles"
386
Problem 386 (solved by 558 members)
Difficulty rating: 40%
"Maximum length of an antichain"
387
Problem 387 (solved by 3078 members)
Difficulty rating: 10%
"Harshad Numbers"
388
Problem 388 (solved by 439 members)
Difficulty rating: 50%
"Distinct Lines"
389
Problem 389 (solved by 1145 members)
Difficulty rating: 30%
"Platonic Dice"
390
Problem 390 (solved by 477 members)
Difficulty rating: 60%
"Triangles with non rational sides and integral area"
391
Problem 391 (solved by 223 members)
Difficulty rating: 75%
"Hopping Game"
392
Problem 392 (solved by 537 members)
Difficulty rating: 35%
"Enmeshed unit circle"
393
Problem 393 (solved by 568 members)
Difficulty rating: 50%
"Migrating ants"
394
Problem 394 (solved by 409 members)
Difficulty rating: 55%
"Eating pie"
395
Problem 395 (solved by 521 members)
Difficulty rating: 40%
"Pythagorean tree"
396
Problem 396 (solved by 495 members)
Difficulty rating: 40%
"Weak Goodstein sequence"
397
Problem 397 (solved by 211 members)
Difficulty rating: 70%
"Triangle on parabola"
398
Problem 398 (solved by 281 members)
Difficulty rating: 55%
"Cutting rope"
399
Problem 399 (solved by 443 members)
Difficulty rating: 45%
"Squarefree Fibonacci Numbers"
400
Problem 400 (solved by 350 members)
Difficulty rating: 55%
"Fibonacci tree game"
401
Problem 401 (solved by 1882 members)
Difficulty rating: 25%
"Sum of squares of divisors"
402
Problem 402 (solved by 287 members)
Difficulty rating: 55%
"Integer-valued polynomials"
403
Problem 403 (solved by 273 members)
Difficulty rating: 55%
"Lattice points enclosed by parabola and line"
404
Problem 404 (solved by 253 members)
Difficulty rating: 60%
"Crisscross Ellipses"
405
Problem 405 (solved by 445 members)
Difficulty rating: 40%
"A rectangular tiling"
406
Problem 406 (solved by 290 members)
Difficulty rating: 50%
"Guessing Game"
407
Problem 407 (solved by 1707 members)
Difficulty rating: 20%
"Idempotents"
408
Problem 408 (solved by 421 members)
Difficulty rating: 50%
"Admissible paths through a grid"
409
Problem 409 (solved by 341 members)
Difficulty rating: 55%
"Nim Extreme"
410
Problem 410 (solved by 214 members)
Difficulty rating: 70%
"Circle and tangent line"
411
Problem 411 (solved by 457 members)
Difficulty rating: 45%
"Uphill paths"
412
Problem 412 (solved by 357 members)
Difficulty rating: 50%
"Gnomon numbering"
413
Problem 413 (solved by 293 members)
Difficulty rating: 75%
"One-child Numbers"
414
Problem 414 (solved by 211 members)
Difficulty rating: 60%
"Kaprekar constant"
415
Problem 415 (solved by 225 members)
Difficulty rating: 100%
"Titanic sets"
416
Problem 416 (solved by 217 members)
Difficulty rating: 80%
"A frog's trip"
417
Problem 417 (solved by 633 members)
Difficulty rating: 35%
"Reciprocal cycles II"
418
Problem 418 (solved by 507 members)
Difficulty rating: 40%
"Factorisation triples"
419
Problem 419 (solved by 378 members)
Difficulty rating: 50%
"Look and say sequence"
420
Problem 420 (solved by 319 members)
Difficulty rating: 60%
"2x2 positive integer matrix"
421
Problem 421 (solved by 448 members)
Difficulty rating: 50%
"+1"
422
Problem 422 (solved by 200 members)
Difficulty rating: 75%
"Sequence of points on a hyperbola"
423
Problem 423 (solved by 337 members)
Difficulty rating: 45%
"Consecutive die throws"
424
Problem 424 (solved by 285 members)
Difficulty rating: 60%
"Kakuro"
425
Problem 425 (solved by 1079 members)
Difficulty rating: 25%
"Prime connection"
426
Problem 426 (solved by 191 members)
Difficulty rating: 75%
"Box-ball system"
427
Problem 427 (solved by 210 members)
Difficulty rating: 95%
"n-sequences"
428
Problem 428 (solved by 183 members)
Difficulty rating: 90%
"Necklace of circles"
429
Problem 429 (solved by 1826 members)
Difficulty rating: 20%
"Sum of squares of unitary divisors"
430
Problem 430 (solved by 639 members)
Difficulty rating: 35%
"Range flips"
431
Problem 431 (solved by 458 members)
Difficulty rating: 40%
"Square Space Silo"
432
Problem 432 (solved by 335 members)
Difficulty rating: 70%
"Totient sum"
433
Problem 433 (solved by 364 members)
Difficulty rating: 65%
"Steps in Euclid's algorithm"
434
Problem 434 (solved by 260 members)
Difficulty rating: 75%
"Rigid graphs"
435
Problem 435 (solved by 753 members)
Difficulty rating: 30%
"Polynomials of Fibonacci numbers"
436
Problem 436 (solved by 328 members)
Difficulty rating: 55%
"Unfair wager"
437
Problem 437 (solved by 550 members)
Difficulty rating: 35%
"Fibonacci primitive roots"
438
Problem 438 (solved by 221 members)
Difficulty rating: 95%
"Integer part of polynomial equation's solutions"
439
Problem 439 (solved by 250 members)
Difficulty rating: 100%
"Sum of sum of divisors"
440
Problem 440 (solved by 257 members)
Difficulty rating: 60%
"GCD and Tiling"
441
Problem 441 (solved by 265 members)
Difficulty rating: 65%
"The inverse summation of coprime couples"
442
Problem 442 (solved by 295 members)
Difficulty rating: 55%
"Eleven-free integers"
443
Problem 443 (solved by 785 members)
Difficulty rating: 30%
"GCD sequence"
444
Problem 444 (solved by 215 members)
Difficulty rating: 60%
"The Roundtable Lottery"
445
Problem 445 (solved by 254 members)
Difficulty rating: 50%
"Retractions A"
446
Problem 446 (solved by 243 members)
Difficulty rating: 60%
"Retractions B"
447
Problem 447 (solved by 185 members)
Difficulty rating: 95%
"Retractions C"
448
Problem 448 (solved by 234 members)
Difficulty rating: 80%
"Average least common multiple"
449
Problem 449 (solved by 638 members)
Difficulty rating: 35%
"Chocolate covered candy"
450
Problem 450 (solved by 153 members)
Difficulty rating: 100%
"Hypocycloid and Lattice points"
451
Problem 451 (solved by 1037 members)
Difficulty rating: 30%
"Modular inverses"
452
Problem 452 (solved by 407 members)
Difficulty rating: 45%
"Long Products"
453
Problem 453 (solved by 162 members)
Difficulty rating: 95%
"Lattice Quadrilaterals"
454
Problem 454 (solved by 343 members)
Difficulty rating: 50%
"Diophantine reciprocals III"
455
Problem 455 (solved by 517 members)
Difficulty rating: 40%
"Powers With Trailing Digits"
456
Problem 456 (solved by 311 members)
Difficulty rating: 50%
"Triangles containing the origin II"
457
Problem 457 (solved by 533 members)
Difficulty rating: 35%
"A polynomial modulo the square of a prime"
458
Problem 458 (solved by 624 members)
Difficulty rating: 30%
"Permutations of Project"
459
Problem 459 (solved by 174 members)
Difficulty rating: 100%
"Flipping game"
460
Problem 460 (solved by 257 members)
Difficulty rating: 55%
"An ant on the move"
461
Problem 461 (solved by 873 members)
Difficulty rating: 30%
"Almost Pi"
462
Problem 462 (solved by 220 members)
Difficulty rating: 60%
"Permutation of 3-smooth numbers"
463
Problem 463 (solved by 790 members)
Difficulty rating: 30%
"A weird recurrence relation"
464
Problem 464 (solved by 211 members)
Difficulty rating: 60%
"Möbius function and intervals"
465
Problem 465 (solved by 160 members)
Difficulty rating: 85%
"Polar polygons"
466
Problem 466 (solved by 220 members)
Difficulty rating: 65%
"Distinct terms in a multiplication table"
467
Problem 467 (solved by 315 members)
Difficulty rating: 50%
"Superinteger"
468
Problem 468 (solved by 190 members)
Difficulty rating: 70%
"Smooth divisors of binomial coefficients"
469
Problem 469 (solved by 518 members)
Difficulty rating: 40%
"Empty chairs"
470
Problem 470 (solved by 169 members)
Difficulty rating: 65%
"Super Ramvok"
471
Problem 471 (solved by 153 members)
Difficulty rating: 75%
"Triangle inscribed in ellipse"
472
Problem 472 (solved by 199 members)
Difficulty rating: 60%
"Comfortable Distance II"
473
Problem 473 (solved by 532 members)
Difficulty rating: 35%
"Phigital number base"
474
Problem 474 (solved by 271 members)
Difficulty rating: 50%
"Last digits of divisors"
475
Problem 475 (solved by 311 members)
Difficulty rating: 50%
"Music festival"
476
Problem 476 (solved by 318 members)
Difficulty rating: 45%
"Circle Packing II"
477
Problem 477 (solved by 188 members)
Difficulty rating: 65%
"Number Sequence Game"
478
Problem 478 (solved by 137 members)
Difficulty rating: 100%
"Mixtures"
479
Problem 479 (solved by 889 members)
Difficulty rating: 25%
"Roots on the Rise"
480
Problem 480 (solved by 412 members)
Difficulty rating: 45%
"The Last Question"
481
Problem 481 (solved by 175 members)
Difficulty rating: 65%
"Chef Showdown"
482
Problem 482 (solved by 154 members)
Difficulty rating: 85%
"The incenter of a triangle"
483
Problem 483 (solved by 140 members)
Difficulty rating: 100%
"Repeated permutation"
484
Problem 484 (solved by 177 members)
Difficulty rating: 100%
"Arithmetic Derivative"
485
Problem 485 (solved by 797 members)
Difficulty rating: 30%
"Maximum number of divisors"
486
Problem 486 (solved by 183 members)
Difficulty rating: 70%
"Palindrome-containing strings"
487
Problem 487 (solved by 424 members)
Difficulty rating: 40%
"Sums of power sums"
488
Problem 488 (solved by 172 members)
Difficulty rating: 80%
"Unbalanced Nim"
489
Problem 489 (solved by 154 members)
Difficulty rating: 100%
"Common factors between two sequences"
490
Problem 490 (solved by 173 members)
Difficulty rating: 90%
"Jumping frog"
491
Problem 491 (solved by 1434 members)
Difficulty rating: 20%
"Double pandigital number divisible by 11"
492
Problem 492 (solved by 232 members)
Difficulty rating: 60%
"Exploding sequence"
493
Problem 493 (solved by 3285 members)
Difficulty rating: 10%
"Under The Rainbow"
494
Problem 494 (solved by 150 members)
Difficulty rating: 100%
"Collatz prefix families"
495
Problem 495 (solved by 152 members)
Difficulty rating: 100%
"Writing n as the product of k distinct positive integers"
496
Problem 496 (solved by 205 members)
Difficulty rating: 50%
"Incenter and circumcenter of triangle"
497
Problem 497 (solved by 338 members)
Difficulty rating: 40%
"Drunken Tower of Hanoi"
498
Problem 498 (solved by 333 members)
Difficulty rating: 40%
"Remainder of polynomial division"
499
Problem 499 (solved by 223 members)
Difficulty rating: 100%
"St. Petersburg Lottery"
500
Problem 500 (solved by 2563 members)
Difficulty rating: 15%
"Problem 500!!!"
501
Problem 501 (solved by 902 members)
Difficulty rating: 40%
"Eight Divisors"
502
Problem 502 (solved by 192 members)
Difficulty rating: 100%
"Counting Castles"
503
Problem 503 (solved by 238 members)
Difficulty rating: 60%
"Compromise or persist"
504
Problem 504 (solved by 2018 members)
Difficulty rating: 15%
"Square on the Inside"
505
Problem 505 (solved by 151 members)
Difficulty rating: 90%
"Bidirectional Recurrence"
506
Problem 506 (solved by 621 members)
Difficulty rating: 30%
"Clock sequence"
507
Problem 507 (solved by 144 members)
Difficulty rating: 90%
"Shortest Lattice Vector"
508
Problem 508 (solved by 157 members)
Difficulty rating: 85%
"Integers in base i-1"
509
Problem 509 (solved by 387 members)
Difficulty rating: 40%
"Divisor Nim"
510
Problem 510 (solved by 738 members)
Difficulty rating: 30%
"Tangent Circles"
511
Problem 511 (solved by 289 members)
Difficulty rating: 55%
"Sequences with nice divisibility properties"
512
Problem 512 (solved by 1029 members)
Difficulty rating: 25%
"Sums of totients of powers"
513
Problem 513 (solved by 229 members)
Difficulty rating: 60%
"Integral median"
514
Problem 514 (solved by 150 members)
Difficulty rating: 90%
"Geoboard Shapes"
515
Problem 515 (solved by 328 members)
Difficulty rating: 40%
"Dissonant Numbers"
516
Problem 516 (solved by 1008 members)
Difficulty rating: 20%
"5-smooth totients"
517
Problem 517 (solved by 343 members)
Difficulty rating: 45%
"A real recursion"
518
Problem 518 (solved by 1068 members)
Difficulty rating: 20%
"Prime triples and geometric sequences"
519
Problem 519 (solved by 261 members)
Difficulty rating: 50%
"Tricolored Coin Fountains"
520
Problem 520 (solved by 288 members)
Difficulty rating: 45%
"Simbers"
521
Problem 521 (solved by 531 members)
Difficulty rating: 45%
"Smallest prime factor"
522
Problem 522 (solved by 178 members)
Difficulty rating: 85%
"Hilbert's Blackout"
523
Problem 523 (solved by 637 members)
Difficulty rating: 30%
"First Sort I"
524
Problem 524 (solved by 157 members)
Difficulty rating: 70%
"First Sort II"
525
Problem 525 (solved by 344 members)
Difficulty rating: 45%
"Rolling Ellipse"
526
Problem 526 (solved by 235 members)
Difficulty rating: 60%
"Largest prime factors of consecutive numbers"
527
Problem 527 (solved by 504 members)
Difficulty rating: 30%
"Randomized Binary Search"
528
Problem 528 (solved by 202 members)
Difficulty rating: 55%
"Constrained Sums"
529
Problem 529 (solved by 147 members)
Difficulty rating: 80%
"10-substrings"
530
Problem 530 (solved by 267 members)
Difficulty rating: 55%
"GCD of Divisors"
531
Problem 531 (solved by 710 members)
Difficulty rating: 25%
"Chinese leftovers"
532
Problem 532 (solved by 220 members)
Difficulty rating: 55%
"Nanobots on Geodesics"
533
Problem 533 (solved by 233 members)
Difficulty rating: 50%
"Minimum values of the Carmichael function"
534
Problem 534 (solved by 221 members)
Difficulty rating: 55%
"Weak Queens"
535
Problem 535 (solved by 217 members)
Difficulty rating: 55%
"Fractal Sequence"
536
Problem 536 (solved by 201 members)
Difficulty rating: 55%
"Modulo power identity "
537
Problem 537 (solved by 397 members)
Difficulty rating: 35%
"Counting tuples"
538
Problem 538 (solved by 239 members)
Difficulty rating: 40%
"Maximum quadrilaterals"
539
Problem 539 (solved by 568 members)
Difficulty rating: 30%
"Odd elimination"
540
Problem 540 (solved by 407 members)
Difficulty rating: 30%
"Counting primitive Pythagorean triples"
541
Problem 541 (solved by 137 members)
Difficulty rating: 90%
"Divisibility of Harmonic Number Denominators"
542
Problem 542 (solved by 162 members)
Difficulty rating: 65%
"Geometric Progression with Maximum Sum"
543
Problem 543 (solved by 448 members)
Difficulty rating: 30%
"Prime-Sum Numbers"
544
Problem 544 (solved by 145 members)
Difficulty rating: 85%
"Chromatic Conundrum"
545
Problem 545 (solved by 347 members)
Difficulty rating: 35%
"Faulhaber's Formulas"
546
Problem 546 (solved by 148 members)
Difficulty rating: 80%
"The Floor's Revenge"
547
Problem 547 (solved by 154 members)
Difficulty rating: 70%
"Distance of random points within hollow square laminae"
548
Problem 548 (solved by 414 members)
Difficulty rating: 35%
"Gozinta Chains"
549
Problem 549 (solved by 1735 members)
Difficulty rating: 10%
"Divisibility of factorials"
550
Problem 550 (solved by 207 members)
Difficulty rating: 55%
"Divisor game"
551
Problem 551 (solved by 322 members)
Difficulty rating: 50%
"Sum of digits sequence"
552
Problem 552 (solved by 283 members)
Difficulty rating: 40%
"Chinese leftovers II"
553
Problem 553 (solved by 145 members)
Difficulty rating: 80%
"Power sets of power sets"
554
Problem 554 (solved by 144 members)
Difficulty rating: 75%
"Centaurs on a chess board"
555
Problem 555 (solved by 472 members)
Difficulty rating: 30%
"McCarthy 91 function"
556
Problem 556 (solved by 151 members)
Difficulty rating: 80%
"Squarefree Gaussian Integers"
557
Problem 557 (solved by 215 members)
Difficulty rating: 55%
"Cutting triangles"
558
Problem 558 (solved by 170 members)
Difficulty rating: 60%
"Irrational base"
559
Problem 559 (solved by 120 members)
Difficulty rating: 95%
"Permuted Matrices"
560
Problem 560 (solved by 180 members)
Difficulty rating: 70%
"Coprime Nim"
561
Problem 561 (solved by 512 members)
Difficulty rating: 30%
"Divisor Pairs"
562
Problem 562 (solved by 137 members)
Difficulty rating: 70%
"Maximal perimeter"
563
Problem 563 (solved by 220 members)
Difficulty rating: 45%
"Robot Welders"
564
Problem 564 (solved by 172 members)
Difficulty rating: 55%
"Maximal polygons"
565
Problem 565 (solved by 400 members)
Difficulty rating: 35%
"Divisibility of sum of divisors"
566
Problem 566 (solved by 99 members)
Difficulty rating: 100%
"Cake Icing Puzzle"
567
Problem 567 (solved by 177 members)
Difficulty rating: 50%
"Reciprocal games I"
568
Problem 568 (solved by 174 members)
Difficulty rating: 50%
"Reciprocal games II"
569
Problem 569 (solved by 282 members)
Difficulty rating: 45%
"Prime Mountain Range"
570
Problem 570 (solved by 190 members)
Difficulty rating: 50%
"Snowflakes"
571
Problem 571 (solved by 699 members)
Difficulty rating: 25%
"Super Pandigital Numbers"
572
Problem 572 (solved by 234 members)
Difficulty rating: 50%
"Idempotent matrices"
573
Problem 573 (solved by 141 members)
Difficulty rating: 75%
"Unfair race"
574
Problem 574 (solved by 190 members)
Difficulty rating: 50%
"Verifying Primes"
575
Problem 575 (solved by 364 members)
Difficulty rating: 35%
"Wandering Robots"
576
Problem 576 (solved by 169 members)
Difficulty rating: 50%
"Irrational jumps"
577
Problem 577 (solved by 947 members)
Difficulty rating: 20%
"Counting hexagons"
578
Problem 578 (solved by 144 members)
Difficulty rating: 75%
"Integers with decreasing prime powers"
579
Problem 579 (solved by 76 members)
Difficulty rating: 100%
"Lattice points in lattice cubes"
580
Problem 580 (solved by 154 members)
Difficulty rating: 70%
"Squarefree Hilbert numbers"
581
Problem 581 (solved by 545 members)
Difficulty rating: 30%
"47-smooth triangular numbers"
582
Problem 582 (solved by 209 members)
Difficulty rating: 45%
"Nearly isosceles 120 degree triangles"
583
Problem 583 (solved by 253 members)
Difficulty rating: 45%
"Heron Envelopes"
584
Problem 584 (solved by 109 members)
Difficulty rating: 95%
"Birthday Problem Revisited"
585
Problem 585 (solved by 80 members)
Difficulty rating: 100%
"Nested square roots"
586
Problem 586 (solved by 145 members)
Difficulty rating: 70%
"Binary Quadratic Form"
587
Problem 587 (solved by 1711 members)
Difficulty rating: 20%
"Concave triangle"
588
Problem 588 (solved by 307 members)
Difficulty rating: 35%
"Quintinomial coefficients"
589
Problem 589 (solved by 120 members)
Difficulty rating: 90%
"Poohsticks Marathon"
590
Problem 590 (solved by 173 members)
Difficulty rating: 60%
"Sets with a given Least Common Multiple"
591
Problem 591 (solved by 122 members)
Difficulty rating: 95%
"Best Approximations by Quadratic Integers"
592
Problem 592 (solved by 185 members)
Difficulty rating: 60%
"Factorial trailing digits 2"
593
Problem 593 (solved by 321 members)
Difficulty rating: 35%
"Fleeting Medians"
594
Problem 594 (solved by 134 members)
Difficulty rating: 85%
"Rhombus Tilings"
595
Problem 595 (solved by 408 members)
Difficulty rating: 35%
"Incremental Random Sort"
596
Problem 596 (solved by 244 members)
Difficulty rating: 50%
"Number of lattice points in a hyperball"
597
Problem 597 (solved by 119 members)
Difficulty rating: 100%
"Torpids"
598
Problem 598 (solved by 309 members)
Difficulty rating: 40%
"Split Divisibilities"
599
Problem 599 (solved by 200 members)
Difficulty rating: 60%
"Distinct Colourings of a Rubik's Cube"
600
Problem 600 (solved by 384 members)
Difficulty rating: 35%
"Integer sided equiangular hexagons"
601
Problem 601 (solved by 1084 members)
Difficulty rating: 20%
"Divisibility streaks"
602
Problem 602 (solved by 296 members)
Difficulty rating: 35%
"Product of Head Counts"
603
Problem 603 (solved by 258 members)
Difficulty rating: 45%
"Substring sums of prime concatenations"
604
Problem 604 (solved by 337 members)
Difficulty rating: 40%
"Convex path in square"
605
Problem 605 (solved by 467 members)
Difficulty rating: 25%
"Pairwise Coin-Tossing Game"
606
Problem 606 (solved by 247 members)
Difficulty rating: 50%
"Gozinta Chains II"
607
Problem 607 (solved by 910 members)
Difficulty rating: 20%
"Marsh Crossing"
608
Problem 608 (solved by 193 members)
Difficulty rating: 80%
"Divisor Sums"
609
Problem 609 (solved by 427 members)
Difficulty rating: 20%
"π sequences"
610
Problem 610 (solved by 345 members)
Difficulty rating: 35%
"Roman Numerals II"
611
Problem 611 (solved by 217 members)
Difficulty rating: 55%
"Hallway of square steps"
612
Problem 612 (solved by 343 members)
Difficulty rating: 30%
"Friend numbers"
613
Problem 613 (solved by 737 members)
Difficulty rating: None%
"Pythagorean Ant"
614
Problem 614 (solved by 199 members)
Difficulty rating: None%
"Special partitions 2"
615
Problem 615 (solved by 325 members)
Difficulty rating: None%
"The millionth number with at least one million prime factors"
616
Problem 616 (solved by 292 members)
Difficulty rating: None%
"Creative numbers"
617
Problem 617 (solved by 234 members)
Difficulty rating: None%
"Mirror Power Sequence"
618
Problem 618 (solved by 371 members)
Difficulty rating: None%
"Numbers with a given prime factor sum"
619
Problem 619 (solved by 208 members)
Difficulty rating: None%
"Square subsets"
620
Problem 620 (solved by 84 members)
Difficulty rating: None%
"Planetary Gears"
621
Problem 621 (solved by 239 members)
Difficulty rating: None%
"Expressing an integer as the sum of triangular numbers"
622
Problem 622 (solved by 262 members)
Difficulty rating: None%
"Riffle Shuffles"

Problem Difficulty Ratings

Difficulty Rating Problems Available Problems Solved Progress
100% 18
95% 9
90% 10
85% 10
80% 22
75% 26
70% 49
65% 34
60% 45
55% 40
50% 59
45% 38
40% 36
35% 44
30% 34
25% 27 1
Completed 3% of problems with difficulty rating 25%
20% 22 1
Completed 4% of problems with difficulty rating 20%
15% 16 1
Completed 6% of problems with difficulty rating 15%
10% 10 6
Completed 60% of problems with difficulty rating 10%
5% 63 63
Completed 100% of problems with difficulty rating 5%
Mean Difficulty 46.76% 6.04%
Highest difficulty solved = 25%