Prime Numbers

A prime number is a number that can only be divided by 1 and itself, without remainder. For example, the number 19 is prime because it can only be divided by 1 and itself:

  • 19 ÷ 1 = 19
  • 19 ÷ 19 = 1

Another prime number is 41, since it can only be divided by 1 and itself:

  • 41 ÷ 1 = 41
  • 41 ÷ 41 = 1

In other words, a prime number has only 2 divisors: 1 and itself.

A composite number is a number that can be divided by more than 2 numbers. 9 is a composite number because it can be divided by 1, 3, and 9:

  • 9 ÷ 1 = 9
  • 9 ÷ 3 = 3
  • 9 ÷ 9 = 1

Another composite number is 24 since it can be divided by 1,2,3,4,6,8,12, and 24:

  • 24 ÷ 1 = 24
  • 24 ÷ 2 = 12
  • 24 ÷ 3 = 8
  • 24 ÷ 4 = 6
  • 24 ÷ 6 = 4
  • 24 ÷ 8 = 3
  • 24 ÷ 12 = 2
  • 24 ÷ 24 = 1

In other words, a composite number has more than 2 divisors.

The number 1 is not considered prime or composite. The smallest positive prime number is 2, which happens to be the only even prime number.

Here are all the prime numbers smaller than 100:

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97