31 (number)

Thirty-one (31 ) is the natural number between thirty and thirty-two. It is odd and a prime number.

Mathematics

Thirty is the third Mersenne prime.

Thirty-one is a centered triangular number, a centered Fünfeckszahl and a centered Zehneckszahl.

For the Steiner tree problem is thirty the number of possible topologies for Steiner Steiner trees with 4 endpoints.

In addition, 3110 is a Devlali number, that is, they can not be generated from the sum of any other integer as well as their numbers.

31, 331, 3331, 33331, 333331, 3333331 and 33,333,331 are all prime numbers. Therefore, it was assumed that each number of the form 3W1 is a prime number. This assumption is refuted today because the next nine examples of this series are not prime:

• 333333331 = 17 × 19,607,843
• 3333333331 = 673 × 4952947
• 33333333331 = 307 × 108 577 633
• 333333333331 = 19 × 83 × 211 371 803
• 3333333333331 = 523 × 3049 × 2090353
• 33333333333331 = 607 × 1511 × 1997 × 18199
• 333333333333331 = 181 × 1841620626151
• 3333333333333331 = 199 × 16,750,418,760,469 and
• 33333333333333331 = 31 × 1499 × 717,324,094,199th

Science

Chemistry

31 is the atomic number of gallium.

Astronomy

• The Andromeda galaxy is listed in the Messier catalog as M31
• NGC 31 is a spiral galaxy in the constellation Phoenix

Culture

Thirty is the name of two gambling with playing cards, namely:

• The old French game Trente -et -un, have emerged from the later Seventeen and four and blackjack and
• The card game swimming.

Trivia

• The number of triads in music ( 12 large, 12 small, 4 and 3 decreased excessive ).
• The number of days of the months of January, March, May, July, August, October and December.
• The international calling code of the Netherlands.
• ISO 31 is an international standard for quantities and units.
• The title of a book by Nick Hornby: " 31 Songs".
• Haute- Garonne is a French department 31.
• Villa 31 slum in Buenos Aires

• Integer