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# 15 (number)

15 (fifteen) is the natural number following 14 and preceding 16.

Cardinal 15
fifteen
Ordinal 15th
fifteenth
Factorization [itex]3 \cdot 5[itex]
Divisors 1, 3, 5, 15
Roman numeral XV
Binary 1111

## In mathematics

Fifteen is a triangular number and a hexagonal number, a pentatope number, and the 4th Bell number. Fifteen is the double factorial of 5. It is a composite number; its proper divisors being 1, 3 and 5. With only two exceptions, all prime quadruplets enclose a multiple of 15, with 15 itself being enclosed by the quadruplet (11, 13, 17, 19).

In hexadecimal, as well as all higher bases, fifteen is represented as F.

Fifteen is the magic constant of the unique order-3 normal magic square:

15 is the smallest number that can be factorized using Shor's quantum algorithm

## The age 15

Age 15 is:

• The age of a quinceaĆ±era, a Hispanic girl celebrating her fifteenth birthday.
• The age for obtaining a driver's (or learner's) permit in jurisdictions where the age for a driver's license is sixteen.
• If you are a boy, under certain circumstances you can be sent to prison to await trial at the age of 15

Fifteen is: