# 90 (number)

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

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Cardinal | ninety | |||

Ordinal | 90th (ninetieth) | |||

Factorization | 2 × 3^{2} × 5 | |||

Divisors | 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90 | |||

Greek numeral | Ϟ´ | |||

Roman numeral | XC | |||

Binary | 1011010_{2} | |||

Ternary | 10100_{3} | |||

Quaternary | 1122_{4} | |||

Quinary | 330_{5} | |||

Senary | 230_{6} | |||

Octal | 132_{8} | |||

Duodecimal | 76_{12} | |||

Hexadecimal | 5A_{16} | |||

Vigesimal | 4A_{20} | |||

Base 36 | 2I_{36} |

In the English language, the numbers 90 and 19 are often confused, as they sound very similar. When carefully enunciated, they differ in which syllable is stressed: 19 /naɪnˈtiːn/ vs 90 /ˈnaɪnti/. However, in dates such as 1999, and when contrasting numbers in the teens and when counting, such as 17, 18, 19, the stress shifts to the first syllable: 19 /ˈnaɪntiːn/.

Look up in Wiktionary, the free dictionary.ninety |

## In mathematicsEdit

**90** is:

- a unitary perfect number because it is the sum of its unitary divisors (excluding itself).
^{[1]} - a semiperfect number because it is equal to the sum of a subset of its divisors.
^{[2]} - a pronic number.
^{[3]} - a nontotient.
^{[4]} - a Perrin number, preceded in the sequence by 39, 51, 68.
^{[5]} - a Harshad number since 90 is divisible by the sum of its base 10 digits.
^{[6]}

In normal space, the interior angles of a rectangle 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.^{[7]} Thus, an angle measuring 90 degrees is called a right angle.^{[8]}

## In scienceEdit

**Ninety** is:

## In sportsEdit

- 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 (27 m) away in distance
- The car number most associated with former NASCAR team owner Junie Donlavey
- The number of minutes in a football (soccer) match.

## In other fieldsEdit

- +90 is the code for international direct dial phone calls to Turkey.
- 90 is the code for the French département Belfort.

## ReferencesEdit

**^**"Sloane's A002827 : Unitary perfect numbers".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**"Sloane's A005835 : Pseudoperfect (or semiperfect) numbers".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**"Sloane's A002378 : Oblong (or promic, pronic, or heteromecic) numbers".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**"Sloane's A005277 : Nontotients".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**"Sloane's A001608 : Perrin sequence".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**"Sloane's A005349 : Niven (or Harshad) numbers".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**http://www.sparknotes.com/testprep/books/newsat/chapter20section4.rhtml**^**Friedman, Erich. What's Special About This Number?