# Is 991 a prime number?

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

For 991, the answer is: yes, 991 is a prime number because it has only two distinct divisors: 1 and itself (991).

As a consequence, 991 is only a multiple of 1 and 991.

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Since 991 is a prime number, 991 is also a deficient number, that is to say 991 is a natural integer that is strictly larger than the sum of its proper divisors, i.e., the divisors of 991 without 991 itself (that is 1, by definition!).