Question

Is 91 a prime number

Answer 1

No, 91 is not a prime number.

The list of all positive divisors (i.e., the list of all integers that divide 91) is as follows: 1, 7, 13, 91.

To be 91 a prime number, it would have been required that 91 has only two divisors, i.e., itself and 1.

As a consequence:
91 is a multiple of 1
91 is a multiple of 7
91 is a multiple of 13

To be 91 a prime number, it would have been required that 91 has only two divisors, i.e., itself and 1.


However, 91 is a semiprime (also called biprime or 2-almost-prime), because it is the product of a two non-necessarily distinct prime numbers.
Indeed, 91 = 7 x 13, where 7 and 13 are both prime numbers.