# Is 855 a prime number?

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

For 855, the answer is: No, 855 is not a prime number.

The list of all positive divisors (i.e., the list of all integers that divide 855) is as follows: 1, 3, 5, 9, 15, 19, 45, 57, 95, 171, 285, 855.

For 855 to be a prime number, it would have been required that 855 has only two divisors, i.e., itself and 1.

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Actually, one can immediately see that 855 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 855 is 5, so it is divisible by 5 and is therefore *not* prime.

As a consequence:

- 855 is a multiple of 1
- 855 is a multiple of 3
- 855 is a multiple of 5
- 855 is a multiple of 9
- 855 is a multiple of 15
- 855 is a multiple of 19
- 855 is a multiple of 45
- 855 is a multiple of 57
- 855 is a multiple of 95
- 855 is a multiple of 171
- 855 is a multiple of 285

For 855 to be a prime number, it would have been required that 855 has only two divisors, i.e., itself and 1.

### Is 855 a deficient number?

Yes, 855 is a deficient number, that is to say 855 is a natural number that is strictly larger than the sum of its proper divisors, i.e., the divisors of 855 without 855 itself (that is 1 + 3 + 5 + 9 + 15 + 19 + 45 + 57 + 95 + 171 + 285 = 705).