From Wikipedia, the free encyclopedia
90 (ninety) is the natural number
preceded by 89 and
followed by 91.
90 

Cardinal 
ninety 
Ordinal 
90th
(ninetieth) 
Numeral
system 
90 
Factorization 

Divisors 
1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90 
Roman numeral 
XC 
Binary 
1011010_{2} 
Octal 
132_{8} 
Duodecimal 
76_{12} 
Hexadecimal 
5A_{16} 
In
mathematics
Because 90 is the sum of its unitary divisors (excluding itself), it
is a unitary perfect number, and
because it is equal to the sum of a subset of its divisors, it is a
semiperfect number. 90 is a pronic number. But
it is also a nontotient. It is a Perrin number, preceded in the sequence
by 39, 51, 68.
In normal space, the interior angles of a square measure 90
degrees each. Also, in a right triangle, the angle opposing the
hypotenuse measures 90 degrees, with the other two angles adding up
to 90 for a total of 180 degrees. Thus, an angle measuring 90
degrees is called a right angle.^{[2]}
90 is divisible by the sum of its base 10 digits, thus it is a
Harshad
number.
In
astronomy
In other
fields
Ninety is:
 The year AD 90, 90 BC, or 1990.
 The 1890’s were known as the Gay Nineties
 Abbott and Costello "The
Naughty Nineties" film (1945)
 The atomic number of thorium, an actinide.
 The atomic weight of an isotope of strontium, a byproduct of nuclear reactions
including fallout. It contaminates milk.
 The latitude of the North Pole and the South Pole.
 The designation of United States Interstate 90, a freeway that runs from
Washington to Massachusetts.
 The code for international direct dial phone calls to Turkey.
 The ISBN Group Identifier for books published in the Netherlands.
 The Russian T90 tank is the most modern in their
arsenal.
 The number of the Psalm credited to Moses; the ninetyfirst
psalm is also likely his work.
 90 minute cassette tapes
 "90 Miles An Hour (Down A Dead End Street)" by Hank Snow
 Mission 90
Days film (2007)
 "Bob Hope: The First
90 Years" TV special aired on NBC on May 14, 1993)
 Joe 90, a 1968 U.K. TV
series, set in 2012
 Playhouse 90,
a 90minute long dramatic CBS TV series from 195661
 Cuba is 90 miles off the Florida coast
 Gloria
Estefan "90 Millas"
CD (90 miles)
 Nokia E90 Communicator
 90 Minutes in Heaven: A True Story of Death and Life by Don Piper
 The number of the French department Territoire de Belfort
 The name (90) of an 1989 album by house music group 808 State.
 "Ninety days delinquent gets you Repo treatment", from Repo! The Genetic Opera.
In sports
See also
References
 ^
Various fanboys and fansites use this nickname. See for example Ninty.net and the South African Nintendo Community.
 ^
Friedman, Erich. What's Special About This
Number?