31

This number is a prime.

Just showing those entries submitted by 'Dobb': (Click here to show all)

(2^31-1)/(2-1) and (2^31+1)/(2+1) are both prime numbers. [Dobb]

The prime number 31 is also a repunit in three different bases: 31 is 11111 in base 2; it is 111 in base 5, and it is 11 in base 30. [Dobb]