The factors of eighty-seven are one, three, twenty-nine, and eighty-seven. Three and twenty-nine are both prime numbers in this case -- there are no other factors.
A factor is one of two or more numbers that when multiplied together will produce a given product. In this instance, the product is eighty-seven. The only factors for eighty-seven are three and twenty-nine and of course one and eighty-seven.
It's important to note though that one is technically not a factor. A factor is either a composite number or a prime number, but due to the fact that the number one is neither composite or prime it cannot be counted as a factor.
Factors are usually found by creating a factorization tree. In a factorization tree a person has the ability to break down a number into various divisible factors. The factorization tree for the number eighty-seven is particularly small though. As mentioned before, the factors for eighty-seven, three and twenty-nine are both prime numbers. There are no numbers that are divisible in either three or twenty-nine, which means that the three is already complete.