Prime or composite

Key Notes:

What is a prime number?

A prime number is a positive whole number with only two factors: 1 and itself.

For example, 7 is a prime number. The only factors of 7 are 1 and 7.

  • 1×7=7

What is a composite number?

A composite number has more factors than just 1 and itself.

For example, 15 is a composite number. It has factors 1, 3, 5, and 15.

  • 3×5=15
  • 1×15=15

Prime and composite numbers chart

This chart shows all of the prime numbers within 200.

A chart with the numbers from two through two hundred is shown. The numbers two, three, five, seven, eleven, thirteen, seventeen, nineteen, twenty-three, twenty-nine, thirty-one, thirty-seven, forty-one, forty-three, forty-seven, fifty-three, fifty-nine, sixty-one, sixty-seven, seventy-one, seventy-three, seventy-nine, eighty-three, eighty-nine, ninety-seven, one hundred one, one hundred three, one hundred seven, one hundred nine, one hundred thirteen, one hundred twenty-seven, one hundred thirty-one, one hundred thirty-seven, one hundred thirty-nine, one hundred forty-nine, one hundred fifty-one, one hundred fifty-seven, one hundred sixty-three, one hundred sixty-seven, one hundred seventy-three, one hundred seventy-nine, one hundred eighty-one, one hundred ninety-one, one hundred ninety-three, one hundred ninety-seven, and one hundred ninety-nine are highlighted to show that they are prime numbers.

Learn with an example

Is 7 a prime number or a composite number?

  • prime number
  • composite number

The only factors of 7 are 1 and 7.
7 is a prime number.

Is 20 a prime number or a composite number?

  • prime number
  • composite number

20 has more factors than just 1 and itself.
For example, 2 is a factor of 20:

20 ÷ 2 = 10
20 is not a prime number.

Is 13 a prime number or a composite number?

  • prime number
  • composite number

The only factors of 13 are 1 and 13.
13 is a prime number.

Let’s practice!✒️