ThirtyOne

Thirty-one is the natural number that follows thirty and precedes thirty-two. In numerals it is written as 31.

In mathematics, thirty-one is a prime number and the eleventh prime. It is also a Mersenne prime, since 31 equals 2^5 minus 1.

In numeral systems other than base ten, thirty-one is 11111 in binary, 37 in octal, and 1F in hexadecimal.

In the calendar, seven months have 31 days: January, March, May, July, August, October, and December; February has 28 days in common years and 29 in leap years.

In culture and business, the name Thirty-One is associated with Proverbs 31 in the Bible, which describes the virtuous woman. The U.S. company Thirty-One Gifts uses the name for its branding and markets handbags and organizational products.

There is also a traditional card game named Thirty-One, played in various regions with different rules.