The mathematical definition of a prime number is a number that has exactly two factors (no more or no less). Commonly though people think of prime numbers as being those that can only be divided exactly by 1 and by the number itself.
The number 7 is not exactly divisible by any number other than 1 and 7
It has two factors only; 1 and 7
Therefore, 7 is a prime number.
In other words, prime numbers have only 2 factors.
The first five prime numbers are; 2 , 3, 5 , 7 , 11
The number 1 has only one factor so 1 is not a prime number.
A natural number that has more than two factors is called a composite number. In other words, a composite number has factors in addition to one and itself.
Number | Factors (or can be exactly divided by) | Composite or Prime? |
2 | 1 , 2 | Prime |
3 | 1 , 3 | Prime |
4 | 1 , 2 , 4 | Composite |
5 | 1 , 5 | Prime |
6 | 1 , 2 , 3 , 6 | Composite |
7 | 1 , 7 | Prime |
8 | 1, 2 , 4 , 8 | Composite |
9 | 1, 3 , 9 | Composite |
10 | 1, 2 , 5 , 10 | Composite |
11 | 1, 11 | Prime |
12 | 1 , 2 , 3 , 6 , 12 | Composite |
13 | 1, 13 | Prime |
14 | 1, 2 , 7 , 14 | Composite |
15 | 1, 3 , 5 , 15 | Composite |
Try our fun Prime or Composite math game (or this other version here) and also have a go at the Factors - Prime and Composite Numbers worksheets below.