Prime numbers

Prime numbers are special numbers that can only be divided by themselves and 1.

19 is a prime number. It can only be divided by 1 and 19.

9 is not a prime number. It can be divided by 3 as well as 1 and 9.

The prime numbers below 20 are:
2, 3, 5, 7, 11, 13, 17, 19

The number 1 is not thought of as a prime number.

Square numbers

A square number is a number multiplied by itself (a number 'squared'; the symbol for squared is ²):

• 1² = 1 x 1 = 1

• 2² = 2…