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Number 31

A page of the Numeropedia - the Special Encyclopedia of Numbers

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[Biology]  The number of pairs of human spinal nerves.

 

[Calendar]  The number of full days in a month (January, March, May, July, August, October and December).

 

[Calendar]  The U.S. Halloween Day is on 31 October.

 

[Chemistry]  The atomic number of Gallium (Ga).

 

[History]  California became the 31st state of the U.S. on 9 September 1850.

 

[History]  The 31st U.S. President: Herbert Clark Hoover (Republican, Iowa, 1929-1933).

His Vice President, Charles Curtis (Kansas), was the 31st U.S. Vice President.

 

[Math.]  A prime number whose digits are the first 2 odd numbers.

 

[Math.]  A truncatable prime number. An absolute prime number (or permutable prime number): both numbers 31 and 13 are prime or in fact, absolute prime.

 

[Math.]  317 = 27,512,614,111 and 2+7+5+1+2+6+1+4+1+1+1 = 31. (ref.15)

 

[Math.]  The 3rd Mersenne prime number: 25–1.

- A Mersenne exponent: 231–1 = 2,147,483,647 is the 8th Mersenne prime number. Hence, 231–1 is the (3rd) double Mersenne number.

 

[Math.]  Reversible numbers and their squares:  132 = 169 and 312 = 961 = 312.

 

[Math.]  162,409 = 169×961 = 4032 = 13×13×31×31.

 

[Math.]  Three square numbers using the same digits: 132 = 169, 142 = 196 and 312 = 961.

 

[Math.] 

13×93 = 1,209 = 31×39

26×93 = 2,418 = 62×39

13×62 =    806 = 31×26.

 

 [Math.]  1/31 = 0.032,258,064,516,129 = 0.032,258,064,516,129,032,258,064,516,129… where multiples of number 32258 are linked together: 032,258×2 = 064,516; 064,516×2 = 129,032, 129,032×2 = 258,064 and 258,064×2+ 1 = 516129 (by rounding up). Similarly for multiples of number 31.

 

[Math.]  A supersingular prime numbers factors of the order of the Monster group M:

246×320×59×76×112×133×17×19×23×29×31×41×47×59×71 =

= 808,017,424,794,512,875,886,459,904,961,710,757,005,754,368,000,000,000.

 

[Phone]  International telephone dialing code for the Netherlands.

 

[Tech.]  The “number system” code of an EAN-13 barcode for France’s products: 30, 31, 32, 33, 34, 35, 36 and 37.

 

[Trivia]  The number of flavors/kinds of ice cream (for every day of a month) at the Baskin-31-Robbins stores (started in 1953).

 

[Trivia]  Ancient Chinese astrologers divided the night sky into 31 regions, namely “Three Enclosures” (Tam Viên) and “Twenty-Eight Mansions” (Nhị Thập Bát Tú). These mansions are grouped by four 7-mansion symbols for four directions: Azure Dragon of the East, Black Tortoise of the North, White Tiger of the West and Vermillion Bird of the South.

 

[World]  The ISO country code for Azerbaijan is 031 (ISO-3166)

 

[Measure]  1 troy ounce = 31.083333 g (grams).

Units for precious metals weight measures: 1 troy pound = 12 troy ounces = 240 pennyweights = 5760 grains = 373 g(grams).