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**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} | |||

Octal | 132_{8} | |||

Duodecimal | 76_{12} | |||

Hexadecimal | 5A_{16} |

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 **ninety** in Wiktionary, the free dictionary.

**90** is:

- a unitary perfect number because it is the sum of its unitary divisors (excluding itself): 1+2+5+9+10+18+45=90.
^{[1]} - a semiperfect number because it is equal to the sum of a subset of its divisors.
^{[2]} - a pronic number: 9 × 10.
^{[3]} - a nontotient.
^{[4]} - a Stirling number of the second kind, the number of ways of dividing a set of six objects into three non empty subsets.
^{[5]} - a Perrin number, preceded in the sequence by 39, 51, 68.
^{[6]} - a Harshad number since 90 is divisible by the sum of its base 10 digits.
^{[7]}

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.^{[8]} Thus, an angle measuring 90 degrees is called a right angle.^{[9]}

**Ninety** is:

- 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) apart.
- The car number most associated with former NASCAR team owner Junie Donlavey

- +90 is the code for international direct dial phone calls to Turkey.
- 90 is the code for the French département Belfort.
- Interstate 90 is a major east-west controlled access highway that spans the continental United States for 3,020 miles from Seattle to Boston.

**^**"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 A008277 :Triangle of Stirling numbers of the second kind".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2021-12-24.**^**"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? Archived 2018-02-23 at the Wayback Machine