Prime numbers are integers, greater than 1, only divisible by themselves and 1 (e.g. 7 and 13)
Composite numbers are also integers greater than 1, which can be divided by at least one other factor, save themselves and 1 (e.g. 50 divides by 50 and 1, but also 25, 2, 5 and 10)
The factors of 34: 34, 1, 17, 2
Of these:
- 2 and 17 are prime
- 34 is composite (it divides by 17 and 2 as well as itself and 1)
- 1 is neither prime nor composite, because it is not greater than 1
The factors of 72: 72, 1, 36, 2, 24, 3, 18, 4, 12, 6, 9, 8
Of these:
- 2 and 3 are prime
- 72, 36, 24, 18, 4, 12, 6, 9 and 8 are composite
- 1 is neither prime nor composite, because it is not greater than 1
For the sake of interest, 6 is a special type of number known as a perfect number. This is because it is equal to the sum of all its integer factors (except for 6 of course!): 1 + 2 + 3 = 6. The next is 28, then 496, then 8128. After this, they become extremely large, because they become increasingly uncommon as you keep counting upwards...
