31 (number) Article Index for
31 		 

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31 (number)
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Cardinal 31
thirty-one
Ordinal 31st
thirty-first
Factorization '' Prime ''
Roman Numeral XXXI
Binary 11111
Hexadecimal 1F



IN MATHEMATICS

Thirty-one is the third Mersenne Prime ( 25 - 1 ) as well as the fourth Primorial Prime , and together with Twenty-nine , another primorial prime, it comprises a Twin Prime . As a Mersenne prime, 31 is related to the Perfect Number 496 , since 496 = 25 - 1 ( 25 - 1). 31 is the eighth Mersenne Prime exponent. 31 is also the fourth Lucky Prime .

31 is a Centered Triangular Number , a Centered Pentagonal Number and Centered Decagonal Number .

At 31, the Mertens Function sets a new low of -4, a value which is not subceded until 110 .

No integer added up to its base 10 digits results in 31, making 31 a Self Number .


IN SCIENCE



Astronomy




  • The series which began on -1805 January 31 and ended on -489 March 31 . The duration of Saros series 31 was 1316.2 years, and it contained 74 solar eclipses.




IN OTHER FIELDS

Thirty-one is also:

  • The number of days in the months January, March, May, July, August, October and December.

  • The code for international direct dial phone calls to the Netherlands .

  • A type of Card Game . See Thirty-one (game) .

  • A type of game played on a Backgammon board.

  • The number of flavors of Baskin Robbins .

  • In '' Star Trek '', the name of Section 31 , a secret police shadow organization of the Federation.

  • ISO 31 is the ISO 's standard for quantities and units

  • In '' Family Guy '', the Griffin house number on Spooner Street

  • In the title of the anime '' Ulysses 31 ''

  • In the title of Nick Hornby's book '' 31 Songs ''

  • Historical years: 31 A.D. , 31 B.C. , or 1931

  • The jersey number of famed NHL goaltender Curtis "CuJo" Joseph, who currently plays for the Phoenix Coyotes.