# Factor

A **factor** is one of the numbers or expressions that make up another number by multiplication. Let a and b be integers. Then a divides b (which may be written a | b ) if there is an integer c such that a * c = b. It is then said that c and a are factors or divisors of b, that b is divisible by c, and that b is a multiple of c.

A number that has no factors other than itself and 1 is a prime number, and a number that has factors other than itself and 1 is called a composite number.