**The factors of 51 are 1, 3, 17 and 51.** Therefore, 51 has a total of four factors. Every number has at least two factors, which include 1 and the number itself.

A factor is a whole number that divides into another number without leaving a remainder. A number with just two factors, 1 and itself, is called a prime number. Numbers that have more than two factors are called composite numbers. Fifty-one can be written as 51 = 1 x 51 or 51 = 3 x 17. Therefore, 51 has four factors – 1, 3, 17 and 51 – since they can factorize 51.