A number may be made by multiplying two or more other numbers together. The numbers that are multiplied together are called factors of the final number.

All numbers have a factor of one since one multiplied by any number equals that number. All numbers can be divided by themselves to produce the number one. Therefore, we normally ignore one and the number itself as useful factors.

Example: The number 15 can be divided into two factors: 3 and 5. This is because 3 times 5 equals 15. Three and five could be called a factor pair of 15.

A number if prime if there are no factor pairs other than 1 and itself.

Some numbers have multiple factor pairs, and you could break them down in different ways. For example, the number 12 has two factor pairs: 2*6 or 3*4.

If you start with 2*6, then you could continue to break apart 6 into its factors of 2*3, so all together, the prime factors of 12 are 2*2*3.

It's the same if you start with 3*4. You could continue to break apart 4 into its factors of 2*2, so all together, the prime factors of 12 are 3*2*2.

You can use the divisibility rules to help you find factors. However, some numbers do not have easy rules, so you may have to use long division or a calculator to check for factors.