# Is 25 a prime number?

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

For 25, the answer is: No, 25 is not a prime number.

The list of all positive divisors (i.e., the list of all integers that divide 25) is as follows: 1, 5, 25.

For 25 to be a prime number, it would have been required that 25 has only two divisors, i.e., itself and 1.

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Actually, one can immediately see that 25 cannot be prime, because 5 is one of its divisors: indeed, a number ending with 0 or 5 has necessarily 5 among its divisors.
The last digit of 25 is 5, so it is divisible by 5 and is therefore *not* prime.

As a consequence:

For 25 to be a prime number, it would have been required that 25 has only two divisors, i.e., itself and 1.

However, 25 is a **semiprime** (also called biprime or 2-almost-prime), because it is the product of a two non-necessarily distinct prime numbers. Indeed, 25 = 5 x 5, where 5 is a prime number.

### Is 25 a deficient number?

Yes, 25 is a deficient number, that is to say 25 is a natural number that is strictly larger than the sum of its proper divisors, i.e., the divisors of 25 without 25 itself (that is 1 + 5 = 6).