Square number

A square number or perfect square is a positive integer of the form n2 where n is a positive integer. They are called square numbers because square numbers of things can be arranged in a square.

Examples
The first 20 square numbers are:

1, 4, 9, 16, 25 36, 49, 64, 81, 100 121, 144, 169, 196, 225 256, 289, 324, 361, 400