ⓘ 90 (number)

ⓘ 90 (number)

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

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/.

1. In mathematics

90 is:

• a nontotient.
• a Perrin number, preceded in the sequence by 39, 51, 68.
• a unitary perfect number because it is the sum of its unitary divisors excluding itself.
• a Harshad number since 90 is divisible by the sum of its base 10 digits.
• a pronic number.
• a semiperfect number because it is equal to the sum of a subset of its divisors.

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. Thus, an angle measuring 90 degrees is called a right angle.

2. In science

Ninety is:

• the atomic number of thorium, an actinide. As an atomic weight, 90 identifies an isotope of strontium, a by-product of nuclear reactions including fallout. It contaminates milk.
• the latitude in degrees of the North and the South geographical poles.

3. In sports

• Major League Baseball bases are 90 feet 27 m away in distance
• The car number most associated with former NASCAR team owner Junie Donlavey
• Nike Total 90 Apparel is a brand name of football apparel and football equipment from equipment bags to goalkeeper gloves
• The number of minutes in a football soccer match.