# Is 51 a prime number?

It is possible to find out using mathematical methods whether a given integer is a prime number or not.

For 51, the answer is: No, 51 is not a prime number.

The list of all positive divisors (i.e., the list of all integers that divide 51) is as follows: 1, 3, 17, 51.

For 51 to be a prime number, it would have been required that 51 has only two divisors, i.e., itself and 1.

Find out more:

As a consequence:

For 51 to be a prime number, it would have been required that 51 has only two divisors, i.e., itself and 1.

However, 51 is a **semiprime** (also called biprime or 2-almost-prime), because it is the product of a two non-necessarily distinct prime numbers. Indeed, 51 = 3 x 17, where 3 and 17 are both prime numbers.

### Is 51 a deficient number?

Yes, 51 is a deficient number, that is to say 51 is a natural number that is strictly larger than the sum of its proper divisors, i.e., the divisors of 51 without 51 itself (that is 1 + 3 + 17 = 21).