**Eight numbers are factors of 40, including 1, 2 and 4.** Other factors of 40 are 5, 8, 10, 20 and 40.

The factors of a number are those that divide evenly into the number in question. To factor a number, it is expressed as a product of smaller numbers which is referred to as factorization. For example, factoring the number 12 would result in 3 x 4, but it can be further factored as 12 = 2 x 2 x 3. If a number can not be factored any further, it is known as a prime number. The greatest common factor is the greatest number that two numbers have in common. For instance, the greatest common factor of 16 and 12 is 4 because it is the largest number that can be evenly divided into both numbers.