What is a prime number?

What is a prime number?

A prime number is any number which only has two factors: 1 and itself.

Examples of prime numbers

• 2 (factors: 1, 2)
• 3 (factors: 1, 3)
• 5 (factors: 1, 5)
• 29 (factors: 1, 29)
• 97 (factors: 1, 97)

Non-examples of prime numbers

• 4 (factors: 1, 2, 4) - three factors
• 6 (factors: 1, 2, 3, 6) - four factors
• 9 (factors: 1, 3, 9) - three factors
• 15 (factors: 1, 3, 5, 15) - four factors
• 1 (factors: 1) - only one factor
• 6.5 - not prime as it is not an integer (whole number)

Composite numbers

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

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