Showing what's behind the curtain

Count the ways a row measuring fifty units in length could be filled with blocks three units long.

Find how many Pythagorean triangles allow tiling with a perimeter < 100,000,000.

The prime factorisation of binomial coefficients

Powers With Trailing Digits

Right triangles with integer coordinates

Finding Nim positions consisting of heap sizes n, 2n and 3n for n ≤ 2^{30} that result in a losing game.

Solve SuDoku puzzles

An unexpected way of using two cubes to make a square.

Comparing four-sided and six-sided dice

Skew-cost coding