The two factors of 17 are 1 and 17. Because 17 only has one set of factors, or factor pair, it is a prime number. This means it can only be divided by 1 and itself.
A factor is a number that can be multiplied to produce another number. In this example, 17 is a prime number because it can only be divided evenly, or without leaving a remainder, by itself and 1. Some other prime numbers are 2, 3, 5, 7, 11, 13 and 19. Composite numbers, on the other hand, have more than one factor pair or factorization.
Factoring is useful in algebra and more advanced mathematics, such as calculus, when dealing with quadratics, trinomials and polynomial equations.