XXXI

XXXI is the Roman numeral for the number 31. It is written as XXXI, with XXX representing thirty and I representing one. Roman numerals use additive notation, where the values of the symbols are summed to form the total.

In mathematics, 31 is a prime number; it is the 11th prime. It is also a Mersenne prime, since 31 equals 2^5 − 1. The binary representation of 31 is 11111.

In the calendar, XXXI commonly appears as the 31st day of a month. Months with 31 days include January, March, May, July, August, October, and December.

In modern culture and events, the roman numeral XXXI is used to denote the 31st edition of events. Notably, the 2016 Summer Olympics in Rio de Janeiro was officially titled the XXXI Olympiad. The designation is part of the tradition of naming editions of recurring events with Roman numerals.

As a numeral, XXXI also appears in inscriptions and numbering schemes to indicate a position in a sequence, such as editions, chapters, or regnal numbers when Roman numerals are used.