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

Mathematics

15 is: * A

composite number A composite number is a positive integer that can be formed by multiplying two smaller positive integers. Equivalently, it is a positive integer that has at least one divisor other than 1 and itself. Every positive integer is composite, prime, ...

, and the sixth

semiprime In mathematics, a semiprime is a natural number that is the product of exactly two prime numbers. The two primes in the product may equal each other, so the semiprimes include the squares of prime numbers. Because there are infinitely many prime nu ...

; its proper

divisor In mathematics, a divisor of an integer n, also called a factor of n, is an integer m that may be multiplied by some integer to produce n. In this case, one also says that n is a multiple of m. An integer n is divisible or evenly divisible by ...

s being , and . * A

deficient number In number theory, a deficient number or defective number is a number ''n'' for which the sum of divisors of ''n'' is less than 2''n''. Equivalently, it is a number for which the sum of proper divisors (or aliquot sum) is less than ''n''. For ex ...

, a

smooth number In number theory, an ''n''-smooth (or ''n''-friable) number is an integer whose prime factors are all less than or equal to ''n''. For example, a 7-smooth number is a number whose every prime factor is at most 7, so 49 = 72 and 15750 = 2 × 32 � ...

, a

lucky number In number theory, a lucky number is a natural number in a set which is generated by a certain "sieve". This sieve is similar to the Sieve of Eratosthenes that generates the primes, but it eliminates numbers based on their position in the remain ...

, a pernicious number, a

bell number In combinatorial mathematics, the Bell numbers count the possible partitions of a set. These numbers have been studied by mathematicians since the 19th century, and their roots go back to medieval Japan. In an example of Stigler's law of eponymy ...

(i.e., the number of partitions for a set of size 4), a

pentatope number A pentatope number is a number in the fifth cell of any row of Pascal's triangle starting with the 5-term row , either from left to right or from right to left. The first few numbers of this kind are: : 1, 5, 15, 35, 70, 126, 210, 330, 4 ...

, and a

repdigit In recreational mathematics, a repdigit or sometimes monodigit is a natural number composed of repeated instances of the same digit in a positional number system (often implicitly decimal). The word is a portmanteau of repeated and digit. Example ...

binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that ta ...

(1111) and

quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

(33). In

hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...

, and higher bases, it is represented as F. * A

triangular number A triangular number or triangle number counts objects arranged in an equilateral triangle. Triangular numbers are a type of figurate number, other examples being square numbers and cube numbers. The th triangular number is the number of dots in ...

, a

hexagonal number A hexagonal number is a figurate number. The ''n''th hexagonal number ''h'n'' is the number of ''distinct'' dots in a pattern of dots consisting of the ''outlines'' of regular hexagons with sides up to n dots, when the hexagons are overlaid so ...

, and a centered tetrahedral number. * The number of partitions of 7. * The smallest number that can be factorized using Shor's quantum algorithm. * The

magic constant The magic constant or magic sum of a magic square is the sum of numbers in any row, column, or diagonal of the magic square. For example, the magic square shown below has a magic constant of 15. For a normal magic square of order ''n'' – that is ...

of the unique order-3 normal magic square. * The number of supersingular primes. 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 (''fif''th) as the prefix. The other such number is 13. *The first 15

superabundant number In mathematics, a superabundant number (sometimes abbreviated as SA) is a certain kind of natural number. A natural number ''n'' is called superabundant precisely when, for all ''m'' < ''n'' :\frac 6/5. Superabundant numbers were defined by . ...

s are the same as the first 15

colossally abundant number In mathematics, a colossally abundant number (sometimes abbreviated as CA) is a natural number that, in a particular, rigorous sense, has many divisors. Formally, a number ''n'' is said to be colossally abundant if there is an ε > 0 su ...

s. * 15 contains the decimal 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 is 27. * There are 15

truncatable prime In number theory, a left-truncatable prime is a prime number which, in a given base, contains no 0, and if the leading ("left") digit is successively removed, then all resulting numbers are prime. For example, 9137, since 9137, 137, 37 and 7 are ...

s which are both right-truncatable and left-truncatable: :2, 3, 5, 7, 23, 37, 53, 73, 313, 317, 373, 797, 3137, 3797, 739397 * There are 15

perfect matching In graph theory, a perfect matching in a graph is a matching that covers every vertex of the graph. More formally, given a graph , a perfect matching in is a subset of edge set , such that every vertex in the vertex set is adjacent to exactl ...

s of the

complete graph In the mathematical field of graph theory, a complete graph is a simple undirected graph in which every pair of distinct vertices is connected by a unique edge. A complete digraph is a directed graph in which every pair of distinct vertices is ...

''K''₆ and 15

rooted binary tree In computer science, a binary tree is a k-ary k = 2 tree data structure in which each node has at most two children, which are referred to as the ' and the '. A recursive definition using just set theory notions is that a (non-empty) binary tr ...

s with four labeled leaves, both of these being among the types of objects counted by double factorials. * With only two exceptions, all

prime quadruplet In number theory, a prime quadruplet (sometimes called prime quadruple) is a set of four prime numbers of the form This represents the closest possible grouping of four primes larger than 3, and is the only prime constellation of length 4. Prim ...

s enclose a multiple of 15, with 15 itself being enclosed by the quadruplet (11, 13, 17, 19). * If a positive definite quadratic form with integer matrix represents all positive integers up to 15, then it represents all positive integers via the 15 and 290 theorems. * 15 is the product of distinct

Fermat prime In mathematics, a Fermat number, named after Pierre de Fermat, who first studied them, is a positive integer of the form :F_ = 2^ + 1, where ''n'' is a non-negative integer. The first few Fermat numbers are: : 3, 5, 17, 257, 65537, 429496 ...

s, 3 and 5; hence a regular

pentadecagon In geometry, a pentadecagon or pentakaidecagon or 15-gon is a fifteen-sided polygon. Regular pentadecagon A ''regular polygon, regular pentadecagon'' is represented by Schläfli symbol . A Regular polygon, regular pentadecagon has interior angl ...

is constructible with compass and unmarked straightedge, and cos is expressible in terms of square roots. * There are 15 monohedral convex pentagonal tilings, with 8 being edge-to-edge. * There are 15 regular and semiregular tilings when infinite (improper) apeirogonal forms are counted: 3 are regular (with one self-dual), 8 are semiregular (with one chiral), and 4 are apeirogonal (from a total of 8, in-which 4 are duplicates). * Full

icosahedral symmetry In mathematics, and especially in geometry, an object has icosahedral symmetry if it has the same symmetries as a regular icosahedron. Examples of other polyhedra with icosahedral symmetry include the regular dodecahedron (the dual polyhedr ...

contains 15 mirror planes (2-fold axes). Specifically, the

symmetry order The symmetry number or symmetry order of an object is the number of different but indistinguishable (or equivalent) arrangements (or views) of the object, that is, it is the order of its symmetry group. The object can be a molecule, crystal latti ...

for both the

regular icosahedron In geometry, a regular icosahedron ( or ) is a convex polyhedron with 20 faces, 30 edges and 12 vertices. It is one of the five Platonic solids, and the one with the most faces. It has five equilateral triangular faces meeting at each vertex. It ...

and

regular dodecahedron A regular dodecahedron or pentagonal dodecahedron is a dodecahedron that is regular, which is composed of 12 regular pentagonal faces, three meeting at each vertex. It is one of the five Platonic solids. It has 12 faces, 20 vertices, 30 ed ...

(which is made of

regular pentagon In geometry, a pentagon (from the Greek πέντε ''pente'' meaning ''five'' and γωνία ''gonia'' meaning ''angle'') is any five-sided polygon or 5-gon. The sum of the internal angles in a simple pentagon is 540°. A pentagon may be simpl ...

s) is 120: equal to sum of the first 15 integers, and the factorial of 5, wherein the sum of the first 5 integers itself is 15. Expressed mathematically: *:

\sum_^i = 120

, while

\sum_^i = 15

, and

5! = 120

. * There are 15

Archimedean solids In geometry, an Archimedean solid is one of the 13 solids first enumerated by Archimedes. They are the convex uniform polyhedra composed of regular polygons meeting in identical vertices, excluding the five Platonic solids (which are compose ...

and 15

Catalan solids Catalan may refer to: Catalonia From, or related to Catalonia: * Catalan language, a Romance language * Catalans, an ethnic group formed by the people from, or with origins in, Northern or southern Catalonia Places * 13178 Catalan, asteroid #13 ...

when

enantiomorphic In chemistry, a molecule or ion is called chiral () if it cannot be superposed on its mirror image by any combination of rotations, translations, and some conformational changes. This geometric property is called chirality (). The terms are d ...

forms are counted separately. * There are 15 regular honeycombs in

hyperbolic Hyperbolic is an adjective describing something that resembles or pertains to a hyperbola (a curve), to hyperbole (an overstatement or exaggeration), or to hyperbolic geometry. The following phenomena are described as ''hyperbolic'' because they ...

3-space: 4 are

compact Compact as used in politics may refer broadly to a pact or treaty; in more specific cases it may refer to: * Interstate compact * Blood compact, an ancient ritual of the Philippines * Compact government, a type of colonial rule utilized in British ...

and 11 are

paracompact In mathematics, a paracompact space is a topological space in which every open cover has an open refinement that is locally finite. These spaces were introduced by . Every compact space is paracompact. Every paracompact Hausdorff space is normal ...

Science

* The

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

. *

Group 15 A pnictogen ( or ; from grc, πνῑ́γω "to choke" and -gen, "generator") is any of the chemical elements in group 15 of the periodic table. Group 15 is also known as the nitrogen group or nitrogen family. Group 15 consists of the ...

of the

periodic table The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...

are sometimes known as the

pnictogen A pnictogen ( or ; from grc, πνῑ́γω "to choke" and -gen, "generator") is any of the chemical elements in group 15 of the periodic table. Group 15 is also known as the nitrogen group or nitrogen family. Group 15 consists of the el ...

s. * 15 Eunomia is the largest Eunomian asteroid in the inner

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, c ...

Religion

Sunnism

The

Hanbali The Hanbali school ( ar, ٱلْمَذْهَب ٱلْحَنۢبَلِي, al-maḏhab al-ḥanbalī) is one of the four major traditional Sunni schools (''madhahib'') of Islamic jurisprudence. It is named after the Arab scholar Ahmad ibn Hanbal ...

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.

Judaism

* In the Hebrew numbering system, the number 15 is not written according to the usual method, with the letters that represent "10" and "5" (י-ה, ''

yodh Yodh (also spelled jodh, yod, or jod) is the tenth letter of the Semitic abjads, including Phoenician Yōd /𐤉, Hebrew Yōd , Aramaic Yod , Syriac Yōḏ ܝ, and Arabic . Its sound value is in all languages for which it is used; in many l ...

'' and '' heh''), because those spell out one of the Jewish names of God. Instead, the date is written with the letters representing "9" and "6" (ט-ו, ''

teth Teth, also written as or Tet, is the ninth letter of the Semitic abjads, including Phoenician Ṭēt , Hebrew Tēt , Aramaic Ṭēth , Syriac Ṭēṯ ܛ, and Arabic . It is the 16th letter of the modern Arabic alphabet. The Persian ṭa ...

'' and '' vav'') *

Passover Passover, also called Pesach (; ), is a major Jewish holidays, Jewish holiday that celebrates the The Exodus, Biblical story of the Israelites escape from slavery in Ancient Egypt, Egypt, which occurs on the 15th day of the Hebrew calendar, He ...

begins on the 15th day of the

Hebrew month The Hebrew calendar ( he, הַלּוּחַ הָעִבְרִי, translit=HaLuah HaIvri), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance, and as an official calendar of the state of Israel. I ...

of Nisan *

Sukkot or ("Booths, Tabernacles") , observedby = Jews, Samaritans, a few Protestant denominations, Messianic Jews, Semitic Neopagans , type = Jewish, Samaritan , begins = 15th day of Tishrei , ends = 21st day of Tishre ...

begins on the 15th day of the

Tishrei Tishrei () or Tishri (; he, ''tīšrē'' or ''tīšrī''; from Akkadian ''tašrītu'' "beginning", from ''šurrû'' "to begin") is the first month of the civil year (which starts on 1 Tishrei) and the seventh month of the ecclesiastical year ...

* Tu Bishvat is a

Jewish holiday Jewish holidays, also known as Jewish festivals or ''Yamim Tovim'' ( he, ימים טובים, , Good Days, or singular , in transliterated Hebrew []), are holidays observed in Judaism and by JewsThis article focuses on practices of mainstre ...

occurring on the 15th of the

Shevat Shevat (Hebrew: שְׁבָט, Standard ''Šəvaṭ'', Tiberian ''Šeḇāṭ''; from Akkadian ''Šabātu'') is the fifth month of the civil year starting in Tishre (or Tishri) and the eleventh month of the ecclesiastical year on the Hebrew cale ...

Modern use

15 is designated as an emergency number in

Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...

, for mobile phones, similar to the international

GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...

emergency number 112; 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 A typical SIM card (mini-SIM with micro-SIM cutout) A GSM mobile phone file:Simkarte NFC SecureElement.jpg, T-Mobile nano-SIM card with NFC capabilities in the SIM tray of an iPhone 6s file:Tf sim both sides.png, A TracFone Wireless SIM card ha ...

in it.

Sports

* In all four of the major Gaelic games— hurling, Gaelic football for

men A man is an adult male human. Prior to adulthood, a male human is referred to as a boy (a male child or adolescent). Like most other male mammals, a man's genome usually inherits an X chromosome from the mother and a Y chro ...

and

women A woman is an adult female human. Prior to adulthood, a female human is referred to as a girl (a female child or Adolescence, adolescent). The plural ''women'' is sometimes used in certain phrases such as "women's rights" to denote female hum ...

, and

camogie Camogie ( ; ga, camógaíocht ) is an Irish stick-and-ball team sport played by women. Camogie is played by 100,000 women in Ireland and worldwide, largely among Irish communities. A variant of the game of hurling (which is played by men onl ...

—each team has 15 players on the field at any given time. * In both major forms of

gridiron football Gridiron football,"Gridiron football"
''Encyclopædia Britannica''. Ret ...

(

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

and

Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...

), standard games are played in 15-minute quarters. * In

rugby union Rugby union, commonly known simply as rugby, is a close-contact team sport that originated at Rugby School in the first half of the 19th century. One of the two codes of rugby football, it is based on running with the ball in hand. In its m ...

: ** Each team has 15 players on the field at any given time, unless one or more players are removed for a serious rules infraction. ** The jersey number 15 is worn by the starting fullback. * In

tennis Tennis is a racket sport that is played either individually against a single opponent ( singles) or between two teams of two players each ( doubles). Each player uses a tennis racket that is strung with cord to strike a hollow rubber ball ...

, the number 15 represents the first point gained in a game. * In

NCAA Division I NCAA Division I (D-I) is the highest level of College athletics, intercollegiate athletics sanctioned by the National Collegiate Athletic Association (NCAA) in the United States, which accepts players globally. D-I schools include the major ...

women's

college basketball In United States colleges, top-tier basketball is governed by collegiate athletic bodies including National Collegiate Athletic Association (NCAA), the National Association of Intercollegiate Athletics (NAIA), the United States Collegiate Athleti ...

, teams are allowed to provide

scholarships A scholarship is a form of financial aid awarded to students for further education. Generally, scholarships are awarded based on a set of criteria such as academic merit, diversity and inclusion, athletic skill, and financial need. Scholarsh ...

to no more than 15 players at any given time. * In

Australian rules football Australian football, also called Australian rules football or Aussie rules, or more simply football or footy, is a contact sport played between two teams of 18 players on an oval field, often a modified cricket ground. Points are scored by k ...

, games in the

AFL Women's AFL Women's (AFLW) is Australia's national semi-professional Australian rules football in Australia, Australian rules football league for women's Australian rules football, female players. The 2017 AFL Women's season, first season of the league ...

league consist of 15-minute quarters. * The maximum number of players on an NBA team roster.

Age 15

* The age of a

quinceañera A (also , , , and ) is a celebration of a girl's 15th birthday. It has pre-Columbian roots in Mexico (Aztecs) and is widely celebrated by girls throughout Latin America. The girl celebrating her 15th birthday is a (; gender (linguistics), ...

, a Latina girl celebrating her 15th birthday. Thus, Spanish

bingo Bingo or B-I-N-G-O may refer to: Arts and entertainment Gaming * Bingo, a game using a printed card of numbers ** Bingo (British version), a game using a printed card of 15 numbers on three lines; most commonly played in the UK and Ireland ** Bi ...

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 legal age for a

driver's license A driver's license is a legal authorization, or the official document confirming such an authorization, for a specific individual to operate one or more types of motorized vehicles—such as motorcycles, cars, trucks, or buses—on a public ...

is 16. * The minimum age for driving a

moped A moped ( ) is a type of small motorcycle, generally having a less stringent licensing requirement than full motorcycles or automobiles. The term used to mean a similar vehicle except with both bicycle pedals and a motorcycle engine. Mopeds typ ...

in some countries. * The age of criminal responsibility in various countries. * In the UK, a minor can be sent to prison to await trial at the age of 15. * In some countries, it is the legal age for

sexual consent Sexual consent is consent to engage in sexual activity. In many jurisdictions, sexual activity without consent is considered rape or other sexual assault. Academic discussion of consent In the late 1980s, academic Lois Pineau argued that societ ...

.Worldwide Ages of Consent
Avert.org. Retrieved on 2011-11-01. * In the UK, it is the legal age to watch a

BBFC The British Board of Film Classification (BBFC, previously the British Board of Film Censors) is a non-governmental organisation founded by the British film industry in 1912 and responsible for the national classification and censorship of fi ...

"15" rated film in a cinema or purchase a "15" rated film or video game. * The

drinking age The legal drinking age is the minimum age at which a person can legally consume alcoholic beverages. The minimum age alcohol can be legally consumed can be different from the age when it can be purchased in some countries. These laws vary between ...

Ethiopia Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...

. * The

age of majority The age of majority is the threshold of legal adulthood as recognized or declared in law. It is the moment when minors cease to be considered such and assume legal control over their persons, actions, and decisions, thus terminating the contr ...

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...

Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...

and

Yemen Yemen (; ar, ٱلْيَمَن, al-Yaman), officially the Republic of Yemen,, ) is a country in Western Asia. It is situated on the southern end of the Arabian Peninsula, and borders Saudi Arabia to the Saudi Arabia–Yemen border, north and ...

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.

References

External links

* – discussing hexadecimals * – discussing the Celtic number as used in Lincolnshire {{Integers, zero Integers