Fifteen
From Halbeeg, the open encyclopedia · Af-Soomaali
1 languages
Fifteen (15) is a natural number that falls between 14 and 16. It consists of two digits when written in the standard decimal system.
The number 15 is a composite number, meaning it has divisors other than 1 and itself. Its divisors are 1, 3, 5, and 15. It can therefore be expressed as 3 × 5, a product of two prime numbers.
Mathematical properties
When its proper divisors less than itself are summed (1 + 3 + 5), the result is 9, which is less than 15. For this reason 15 is classified as a deficient number. It is also a triangular number, since it equals the sum 1 + 2 + 3 + 4 + 5.
In binary notation, 15 is written as 1111, consisting of four ones. This makes it significant in computer arithmetic: 15 is the largest value representable with four bits, and corresponds to the single hexadecimal digit F.
General use
The number 15 appears in timekeeping: a quarter hour is fifteen minutes. It is also used to divide an hour and a minute into four equal parts.
Somali language
In Somali, numbers above ten are formed using an additive system: toban iyo shan (ten and five) or shan iyo toban (five and ten). Both forms are used, though shan iyo toban is more common in everyday speech in many regions.