For the year A.D. 31, see 31.


Thirty-one (31, XXXI) is the natural number following thirty and preceeding thirty-two. It is a prime number, the third Mersenne prime as well as a primorial prime, and together with twenty-nine, another primorial prime, it comprises a twin prime.

Thirty-one is also:


List of numbers

Twenty-nine - Thirty - Thirty-one - Thirty-two - Thirty-three

Integer