Prime Numbers

A prime number is a number which can only be divided by 1 or itself.

The smallest prime number is 2.

2 can only be divided by 2 or 1.

Here are the first 20 prime numbers: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71.

Some numbers you may not be sure about, for example: 51. In this case, try dividing by 3 or 7.

e.g. 51 ÷ 3 = 17

So 51 is not a prime number.

Square Numbers

A square number is formed by multiplying a number by itself.

For example, 2 x 2 = 4.

4 is a square number.

Here are the first ten square numbers: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100.

The square root of a square number is an integer (a whole number).

For example, the square root of 16 is 4.

The meaning of square root is, ‘that figure which multiplied by itself gives the number'. So, 4 is the square root of 16 because 4 x 4 = 16. The symbol for square root is  for example 16 = 4.

Back to top

Cubic Numbers

A cubic number is formed by multiplying a number by itself three times.

For example, 2 x 2 x 2 = 8.

8 is a cubic number.

The first five cubic numbers are: 1, 8, 27, 64, 125.

Back to top

Factors

Factors are numbers which will divide into a number without any remainder.

Example 1: Factors of 12 are 1, 2, 3, 4, 6 and 12, because:

12 ÷ 1 = 12
12 ÷ 2 = 6
12 ÷ 3 = 4
12 ÷ 4 = 3
12 ÷ 6 = 2
12 ÷ 12 = 1

Example 2: Factors of 20 = 1, 2, 4, 5, 10 and 20.

Note: All prime numbers have only two factors i.e. 1 and themselves.

For example, factors of 7 = 1 and 7 only.

Back to top

Multiples

Multiples are formed by multiplying by any number.

Multiples of 5 = 5, 10, 15, 20, etc.

Because 5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20

Reciprocal simply means ‘one over.’

For example, the reciprocal of 4 is ¼.

Back to top
Print this page