91 (number)

From Wikipedia, the free encyclopedia

91 (ninety-one) is the natural number following 90 and preceding 92.

<< 90 91 92 93 94 95 96 97 98 99 >> List of numbers -- Integers 0 10 20 30 40 50 60 70 80 90 >>
Cardinal	91 ninety-one
Ordinal	91st ninety-first
Factorization
Divisors	1, 7, 13, 91
Roman numeral	XCI
Binary	1011011
Hexadecimal	5B

[edit] In mathematics

Ninety-one is a triangular number and a hexagonal number, one of the few such numbers to also be a centered hexagonal number, and it is also a centered nonagonal number and a centered cube number. It is the sum of the squares of the first six integers.

It is the smallest positive integer expressible as a sum of two cubes in two different ways if negative roots are allowed: 91 = 6³+(-5)³ = 4³+3³. (See 1729 for more details).

It is also the smallest pseudoprime satisfying the congruence 3ⁿ = 3 mod n.

91 is a repdigit in base 9 (111).

[edit] In science

• The atomic number of protactinium, an actinide.

In astronomy,

Messier object M91, a magnitude 11.5 spiral galaxy in the constellation Coma Berenices

The New General Catalogue object NGC 91, a single star in the constellation Andromeda

The Saros number of the solar eclipse series which began on August 6, 159 BC and ended on 1175 October 16. The duration of Saros series 91 was 1334.2 years, and it contained 75 solar eclipses.

The Saros number of the lunar eclipse series which began on 161 May 26 and ended on 1459 July 15. The duration of Saros series 91 was 1298.1 years, and it contained 73 lunar eclipses.

[edit] In other fields

Ninety-one is also:

• The designation of American Interstate 91, a freeway that runs from Connecticut to Vermont.
• The code for international direct dial phone calls to India.
• In cents of a U.S. dollar, the amount of money one has if one has one each of the coins of denominations less than a dollar (penny, nickel, dime, quarter and half dollar).
• The ISBN Group Identifier for books published in Sweden.
• The year AD 91, 91 BC, or 1991.
• The jersey number worn by Dennis Rodman with the Chicago Bulls and Tim Spooneybarger with the Florida Marlins.