90 (ninety) is the natural number preceded by 89 and followed by 91.

← 89 91 → 90
← 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	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	10110102
Octal	1328
Duodecimal	7612
Hexadecimal	5A16

Look up ninety in Wiktionary, the free dictionary.

[edit] 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.

[edit] In astronomy

• Messier object M90, a magnitude 11.0 spiral galaxy in the constellation Virgo
• The New General Catalogue object NGC 90, a barred spiral galaxy in the constellation Andromeda
• The Saros number of the solar eclipse series which began on 134 BC September 28 and ended on 1345 March 4. The duration of Saros series 90 was 1478.4 years, and it contained 83 solar eclipses.
• The Saros number of the lunar eclipse series which began on 150 June 27 and ended on 1430 August 4. The duration of Saros series 90 was 1280.1 years, and it contained 72 lunar eclipses.

[edit] In other fields

Interstate 90

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 by-product 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 T-90 tank is the most modern in their arsenal.
• The number of the Psalm credited to Moses; the ninety-first 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 90-minute long dramatic CBS TV series from 1956-61
• 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.

[edit] In sports

• Nike Total 90 Apparel is a brand name of football apparel and football equipment from equipment bags to goalkeeper gloves
• Major League baseball bases are 90 feet away in distance
• The car number most associated by former NASCAR team owner Junie Donlavey
• The number of minutes in a football (soccer) match.

[edit] See also

Mathematics portal

[edit] References

1. ^ Various fanboys and fansites use this nickname. See for example Ninty.net and the South African Nintendo Community.
2. ^ Friedman, Erich. What's Special About This Number?