For the given numbers:
1 = 1^2
4 = 2^2
9 = 3^2
16 = 4^2
25 = 5^2
(The " ^2 " means raised to the power of 2) The numbers 1, 4, 9, 16, and 25 are called perfect squares because if you take the square root of the numbers given, the result is an integer.