90 (number)

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

In mathematics

Ninety is the sums of the squares of the integers 2 to 6. Because 90 is the sum of its unitary divisors (excluding itself), it is a unitary perfect number. 90 is a pronic number. And because 90 is divisible by the sum of its digits in base 10, it is a Harshad number. But it is also a nontotient.

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.

In other fields

Ninety is:

• The atomic number of thorium, an actinide.
• The designation of American 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 year AD 90, 90 BC, or 1990.

es:Noventa it:Novanta ja:90 sl:90 (število) sv:90 (tal) zh:90