15 (
fifteen) is the
natural number following
14 and preceding
16.
In English, it is the smallest natural number with seven letters in
its spelled name.
In speech, the numbers 15 and 50 are often confused. When carefully
enunciated, they differ in which syllable is
stressed: 15 vs 50 . However, in dates
such as 1500 ("fifteen hundred") or when contrasting numbers in the
teens, the stress generally shifts to the first syllable: 15
.
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 , and . With only two exceptions, all
prime quadruplets enclose a
multiple of 15, with 15 itself being enclosed by the quadruplet
(11, 13, 17, 19). 15 is also the number of
supersingular primes.
15 is the 4th discrete
biprime (3.5) and the
first member of the (3.q) discrete
biprime
family. The number proceeding 15;
14 is
itself a discrete
biprime and this is the
first such pair of discrete
biprimes. The
next example is the pair commencing
21.
The aliquot sum of 15 is
9, a square
prime 15 has an aliquot sequence of 6 members (15,9,4,3,1,0).15 is
the fourth composite number in the 3-aliquot tree. The
abundant 12 is
also a member of this tree. Fifteen is the aliquot sum of the
consecutive 4-power
16, and the discrete
biprime 33.
15 and 16 form a
Ruth-Aaron pair
under the second definition in which repeated prime factors are
counted as often as they occur.
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.
There are 15 solutions to
Znám's
problem of length 7.
15 is a
repdigit in
binary (1111). In
hexadecimal, as well as all higher bases,
fifteen is represented as F.
In science
In religion
In Sports
- In tennis, the number 15 represents the
first point gained in a game.
- In Rugby Union the full back wears
the number 15, it is also the number of players on the field.
The age 15
Age 15 is:
- The age of a quinceañera, a
Hispanic girl celebrating her fifteenth birthday. Thus, Spanish bingo callers might refer to the
number 15 as la niña bonita (the beautiful girl).
- The age for obtaining a driver's (or learner's) permit in
certain jurisdictions, including some where the age for a driver's
license is sixteen.
- In the
UK a minor can be sent to
prison to await trial at the age of 15.
- In most cultures 15 is when adulthood officially begins, from
this age onwards (till 18 due to legal rights, or as a general
marker into ones mid to late twenties, and sometimes early 30s.)
they are called young adults.
- In
Sweden and Denmark it's the
legal age for sexual
intercourse.
- In the
UK it is the legal age to watch a BBFC "15" rated film in
a cinema or purchase a "15" rated film or video game.
In other fields
Fifteen is:
- The number 15 is a major theme for the Marilyn Manson album Mechanical Animals, which refers to the
number numerous times.
- 15 is also a song on the Marilyn
Manson album The High End of
Low .
- The number of days in each of the 24 cycles of the Chinese calendar.
- The number of guns in a gun salute to
Army, Marine Corps, and Air Force Lieutenant Generals, and Navy and
Coast Guard Vice Admirals.
- The
designation of Interstate 15, a
freeway that runs from California to Montana.
- The designation of U.S.
Route 15, a highway that runs from South Carolina to New
York.
- The '15 refers to the first Jacobite
Rising in Great Britain in 1715.
- The number of checkers each side has in
the beginning of a backgammon game.
- The 15 puzzle.
- Fifteen, a television
program.
- A
restaurant in London, built by
celebrity chef Jamie Oliver
- In the United States, the customary percentage to tip a
waitress in a restaurant by one or two guests
- 15 minutes of fame
- The 15th is a Wire song
- The number of balls in the eight ball
variant of billiards
- The number of function keys on most Mac keyboards
- The name of a modern punk band, Fifteen
- The number of letters in the words "uncopyrightable", "dermatoglyphics", "misconjugatedly", and
"hydropneumatics", which are the longest words there are without
repeating a letter.
- 15 is one of The
Numbers - 4, 8, 15, 16, 23, and 42 - featured in Lost.
- The number of completed, numbered symphonies and string
quartets by Dmitri
Shostakovich
- A film rating and age limit on viewing given by the British Board of Film
Classification
- The
number to dial for SAMU in case of an emergency
in France.
- 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.
- Fifteen men on the dead man's
chest is the first verse of the chorus of a fictional sea shanty from Robert Louis Stevenson's novel
Treasure Island
(1883),
- 15 Step is the opening song on the
Radiohead album, In
Rainbows.
- In casual conversation, an arbitrary number used to refer to a
large quantity of things. Often prefixed with "like". Greg Oden - 15 titles, Katharine McPhee - 15 babies, 15 Terminators
- The number of the French department Cantal
- Fifteen is a song on Taylor Swift's 2008 album
Fearless
- 15 is a song on Rilo Kiley's 2007
album Under the Blacklight
- The number corresponding to The Devil
in tarot cards.
- Fifteen is the title of a 1956 novel by Beverly Cleary.
Historical years
15 A.D.,
15
B.C.,
1915,
2015,
References
- Wells, D. The Penguin Dictionary of Curious and Interesting
Numbers London: Penguin Group. (1987): 91 - 93