The number 87 is not a prime number. The factors of 87 are 1, 3 and 29. A prime number must have only two factors, the numbers one and the number itself.
To find out whether any given number is a prime number, its factors must be obtained. Numbers that have more than two factors are called composite numbers. All even numbers are divisible by two, and hence all even numbers, except the number two, are composite numbers. The number two is the only even prime number and the smallest prime number. The number one is neither prime nor composite.