What is a composite number?

What is a composite number?

A composite number is any number which has more than two factors.

Examples of composite numbers

• 4 (factors: 1, 2, 4)
• 6 (factors: 1, 2, 3, 6)
• 9 (factors: 1, 3, 9)
• 15 (factors: 1, 3, 5, 15)
• 100 (factors: 1, 2, 4, 5, 10, 20, 25, 50, 100)

Non-examples of composite numbers

• 2 (factors: 1, 2) - only two factors, so it is prime
• 3 (factors: 1, 3) - only two factors, so it is prime
• 5 (factors: 1, 5) - only two factors, so it is prime
• 29 (factors: 1, 29) - only two factors, so it is prime
• 97 (factors: 1, 97) - only two factors, so it is prime
• 1 (factors: 1) - only one factor, so it is neither prime nor composite

Prime numbers

You may think that all non-composite numbers are prime numbers, and you’d be right… usually.

The number 1 has only one factor: 1, so it is not composite because it does not have more than 2 factors.
It is also not prime, because prime numbers have exactly 2 factors.