In 1983 the prolific conjecturer Paul Erdős posed a math problem: Take any set of numbers you like. These could be the whole numbers from 1 to 12, the first 10,000 prime numbers, or the dates of every ...

Using only the numbers 1, 2, 3, and 4, arrange four sets of these numbers into a four-by-four array so that no column or row contains the same two numbers. The result is known as a Latin square ...

A rectangle of size 5 × 7 in the multiplication table. This rectangle has length 7 and height 5, and the area (the number of green squares) is found in the blue circle in the bottom right corner ...