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  • Problem 637 will be accessible in 6 hours, 2 minutes (Sunday, 23rd September 2018, 01:00 am)

The problems archives table shows problems 1 to 626. If you would like to tackle the 10 most recently published problems then go to Recent problems.
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IDDescription / TitleSolved By
151Paper sheets of standard sizes: an expected-value problem
4467
152Writing 1/2 as a sum of inverse squares
2071
153Investigating Gaussian Integers
2046
154Exploring Pascal's pyramid
2078
155Counting Capacitor Circuits
2859
156Counting Digits
1872
157Solving the diophantine equation 1/a+1/b= p/10n
2117
158Exploring strings for which only one character comes lexicographically after its neighbour to the left
2917
159Digital root sums of factorisations
2641
160Factorial trailing digits
2773
161Triominoes
1633
162Hexadecimal numbers
4458
163Cross-hatched triangles
1428
164Numbers for which no three consecutive digits have a sum greater than a given value
4695
165Intersections
2049
166Criss Cross
3283
167Investigating Ulam sequences
1339
168Number Rotations
2113
169Exploring the number of different ways a number can be expressed as a sum of powers of 2
4134
170Find the largest 0 to 9 pandigital that can be formed by concatenating products
1551
171Finding numbers for which the sum of the squares of the digits is a square
2189
172Investigating numbers with few repeated digits
3072
173Using up to one million tiles how many different "hollow" square laminae can be formed?
7648
174Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements
4897
175Fractions involving the number of different ways a number can be expressed as a sum of powers of 2
1420
176Right-angled triangles that share a cathetus
1516
177Integer angled Quadrilaterals
984
178Step Numbers
2722
179Consecutive positive divisors
9466
180Rational zeros of a function of three variables
1233
181Investigating in how many ways objects of two different colours can be grouped
1590
182RSA encryption
2116
183Maximum product of parts
3886
184Triangles containing the origin
1263
185Number Mind
2525
186Connectedness of a network
2300
187Semiprimes
9446
188The hyperexponentiation of a number
5387
189Tri-colouring a triangular grid
1649
190Maximising a weighted product
3434
191Prize Strings
5890
192Best Approximations
1249
193Squarefree Numbers
2631
194Coloured Configurations
1095
195Inscribed circles of triangles with one angle of 60 degrees
1070
196Prime triplets
2031
197Investigating the behaviour of a recursively defined sequence
4160
198Ambiguous Numbers
861
199Iterative Circle Packing
1522
200Find the 200th prime-proof sqube containing the contiguous sub-string "200"
1863