In general, a number or algebraic expression is a factor (or divisor) of another if there exists a number or algebraic expression of a specified type for which
A natural number is a factor of a natural number if there is a natural number such that
For example, is a factor of 12 because
A polynomial is divisible by a polynomial if there is a polynomial for which
For example, is a factor because .
A prime factor of a natural number is a factor of that is a prime number.
For example, the prime factors of are