90 (number)

90 (ninety) is the natural number following 89 and preceding 91.

Mathematics:

• 90 degrees represents a right angle.
• A quarter circle comprises 90 degrees.
• It is a Harshad number in base 10.
• It is a composite number, its proper divisors being 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, and 45.
• It is the sum of four consecutive prime numbers (17 + 19 + 23 + 31).

Other fields:

• The atomic number of Thorium is 90.
• Many countries have a speed limit of 90 kilometers per hour on rural roads or highways.
• In some sports, such as darts, 90 is a scoring achievement.