90 (number): Wikis

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Encyclopedia

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

90
Cardinal ninety
Ordinal 90th
(ninetieth)
Numeral system 90
Factorization $2 \cdot 3^2 \cdot 5$
Divisors 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90
Roman numeral XC
Binary 10110102
Octal 1328
Duodecimal 7612

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.

90 is divisible by the sum of its base 10 digits, thus it is a Harshad number.

In other fields  Interstate 90

Ninety is:

In sports Mathematics portal

References

1. ^ Various fanboys and fansites use this nickname. See for example Ninty.net and the South African Nintendo Community.