What is a composite number?

Answer 1

A composite number is an integer having more than two factors that are whole numbers.

(Factors are two numbers that multiply together to give the number.) Some examples may help to get things in focus.

• 2 has only two factors (1, 2) so it is not a composite number, it is a prime number.
• 3 has only two factors (1, 3) so it is not a composite number, it is a prime number.
• 4 has three factors (1,2,4) so it is a composite number.
• 5 has only two factors (1,5) so it is not a composite number, it is a prime number.
• 6 has four factors (1,2,3,6) so it is a composite number.

Another description:

A composite number is an integer that is exactly divisible by at least one factor other than 1 and itself. There is an infinite number of composite numbers. It is not a Prime number.

A prime number on the other hand has two distinct factors and can only be divided by 1 and itself.

It's easy enough to infer that a composite number can be written as a product of prime factors:

Example 2380 = 2 x 2 x 5 x 7 x 17

The Fundamental Theorem of Arithmetic states that any integer greater than 1 can be written as a unique product of prime numbers. This is a very important theory in math!

The first few composite numbers are: 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20.
A number that is divisible.

Example: 145 is a composite number because you can divide it by 5 and other numbers.

Answer 2

A composite number is a product [multiple] of two or more numbers that are greater than 1.

Answer 3

A composite number is a product of two or more prime numbers. It is a number that has a factor other than 1 and itself.