# 15 (number)

 ← 14 15 16 →
Cardinalfifteen
Ordinal15th
(fifteenth)
Factorization3 × 5
Divisors1, 3, 5, 15
Greek numeralΙΕ´
Roman numeralXV
Binary11112
Ternary1203
Senary236
Octal178
Duodecimal1312
Hebrewט"ו (Tet Vav)

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

## Mathematics

M = 15
The 15 perfect matchings of K6

15 is:

Furthermore,

• 15 is one of two numbers within the teen numerical range (13-19) not to use a single-digit number in the prefix of its name (the first syllable preceding the teen suffix); instead, it uses the adjective form of five (fifth) as the prefix. The other such number is 13.
• The first 15 superabundant numbers are the same as the first 15 colossally abundant numbers.
• In decimal, 15 contains the digits 1 and 5 and is the result of adding together the integers from 1 to 5 (1 + 2 + 3 + 4 + 5 = 15). The only other number with this property (in decimal) is 27.
• There are 15 truncatable primes that are both right-truncatable and left-truncatable:
2, 3, 5, 7, 23, 37, 53, 73, 313, 317, 373, 797, 3137, 3797, 739397 (sequence A020994 in the OEIS)

## Science

Seashells from the mollusk Donax variabilis have 15 coloring pattern phenotypes.

## Religion

### Sunnism

The Hanbali Sunni madhab states that the age of fifteen of a solar or lunar calendar is when one's taklif (obligation or responsibility) begins and is the stage whereby one has his deeds recorded.[5]

## Modern use

15 is designated as an emergency number in Pakistan, for mobile phones, similar to the international GSM emergency number 112;[6] if 112 is used in Pakistan, then the call is routed to 15. 112 can be used in an emergency even if the phone is locked and does not have a SIM card in it.[citation needed]

## Music

• "Fifteen" is a song composed by Taylor Swift on her album Fearless

## In other fields

Fifteen is:

• The 15 puzzle.
• The number of minutes in one quarter of an hour; 15 minutes past or before an hour is often known as quarter past and quarter to, respectively.