90 (number)

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

List of numbers — Integers << 90 91 92 93 94 95 96 97 98 99 >>
Cardinal	ninety
Ordinal	90th (ninetieth)
Factorization	<math>2 \cdot 3^2 \cdot 5<math>
Divisors	2, 3, 5, 6, 9, 15, 18, 30, 45
Roman numeral	XC
Binary	1011010
Hexadecimal	5A

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 year AD 90, 90 BC, or 1990.