91 (
ninety-one) is the
natural number following
90 and preceding
92.
In mathematics
Ninety-one is the twenty-seventh distinct
biprime and the second of the form (7.q). The
aliquot sum of
91 is
21 within the aliquot sequence (91,21,11,1,0)
91 being the fourth composite number in the
11-aliquot tree.
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 a
square pyramidal number,
being 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 =
6
^{3}+(-5)
^{3} = 4
^{3}+3
^{3}. (See
1729 for more details).
It is also the smallest
pseudoprime
satisfying the congruence 3
^{n} = 3 mod
n.
91 is a
repdigit in base 9 (111).
In science
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. 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 and ended on 1459 July.
The duration of Saros series 91 was 1298.1 years, and it contained
73 lunar eclipses.
In other fields
Ninety-one is also:
- The year AD 91, 91 BC, or 1991.
- The
designation of American Interstate 91, a freeway that runs from
Connecticut to Vermont
- The designation of U.S. Route 91, a
north-south highway that runs from Utah to Idaho
- 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.
- Psalm 91 is known as the Psalm of
Protection. It is also the title of a book by Peggy Joyce Ruth
- 91 is a solitaire card game where the
object is to move cards, so the top cards total 91.
- STS-91 Space Shuttle Discovery mission to
the International Space
Station, June 2, 1998
- Swedish comic strip
91:an
- The
91st Space Wing (91 SW) is a
Minuteman III unit of the
United States Air Force,
based at Minot Air Force
Base, North
Dakota
- The
number of the French department Essonne
In sports
Bandy
MLB
NBA
NFL
NHL
WNBA
References