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, a smooth number, 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 remaini ...

, a

pernicious number In number theory, a pernicious number is a positive integer such that the Hamming weight of its binary representation is prime, that is, there is a prime number of 1's when it is written as a binary number. Examples The first pernicious number is ...

, a bell number (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, 495 ...

, and a repdigit in

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 t ...

(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, and a

centered tetrahedral number A centered tetrahedral number is a centered figurate number that represents a tetrahedron In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, ...

. * 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 exactly ...

s of the complete graph ''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 factorial In mathematics, the double factorial or semifactorial of a number , denoted by , is the product of all the integers from 1 up to that have the same parity (odd or even) as . That is, :n!! = \prod_^ (n-2k) = n (n-2) (n-4) \cdots. For even , the ...

s. * With only two exceptions, all prime quadruplets 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 In mathematics, the 15 theorem or Conway–Schneeberger Fifteen Theorem, proved by John H. Conway and W. A. Schneeberger in 1993, states that if a positive definite quadratic form with integer matrix represents all positive integers up to 15, th ...

. * 15 is the product of distinct Fermat primes, 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 pentadecagon'' is represented by Schläfli symbol . A regular pentadecagon has interior angles of 156 °, and with a side l ...

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 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 lattic ...

for both the regular icosahedron and regular dodecahedron (which is made of regular pentagons) is 120: equal to sum of the first 15 integers, and the

factorial In mathematics, the factorial of a non-negative denoted is the product of all positive integers less than or equal The factorial also equals the product of n with the next smaller factorial: \begin n! &= n \times (n-1) \times (n-2) \t ...

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 and 15 Catalan solids when enantiomorphic forms are counted separately. * There are 15 regular honeycombs in hyperbolic

3-space Three-dimensional space (also: 3D space, 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called ''parameters'') are required to determine the position of an element (i.e., point). This is the informa ...

: 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.

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 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 ele ...

s. *

15 Eunomia Eunomia (minor planet designation 15 Eunomia) is a very large asteroid in the inner asteroid belt. It is the largest of the stony ( S-type) asteroids, with 3 Juno as a close second. It is quite a massive asteroid, in 6th to 8th place (to withi ...

is the largest Eunomian asteroid in the inner asteroid belt.

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 lan ...

'' 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'' 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 ...

Nisan Nisan (or Nissan; he, נִיסָן, Standard ''Nīsan'', Tiberian ''Nīsān''; from akk, 𒊬𒊒𒄀 ''Nisanu'') in the Babylonian and Hebrew calendars is the month of the barley ripening and first month of spring. The name of the month is ...

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 calend ...

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 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 in it.

Sports

* In all four of the major

Gaelic games Gaelic games ( ga, Cluichí Gaelacha) are a set of sports played worldwide, though they are particularly popular in Ireland, where they originated. They include Gaelic football, hurling, Gaelic handball and rounders. Football and hurling, the ...

—

hurling Hurling ( ga, iománaíocht, ') is an outdoor team game of ancient Gaelic Irish origin, played by men. One of Ireland's native Gaelic games, it shares a number of features with Gaelic football, such as the field and goals, the number of p ...

, Gaelic football for men 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 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 league consist of 15-minute quarters. * The maximum number of players on an

NBA The National Basketball Association (NBA) is a professional basketball league in North America. The league is composed of 30 teams (29 in the United States and 1 in Canada) and is one of the major professional sports leagues in the United St ...

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 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 typic ...

in some countries. * The

age of criminal responsibility The age of criminal responsibility is the age below which a child is deemed incapable of having committed a criminal offence. In legal terms, it is referred to as a defence/defense of infancy, which is a form of defense known as an excuse so tha ...

in various countries. * In the UK, a

minor Minor may refer to: * Minor (law), a person under the age of certain legal activities. ** A person who has not reached the age of majority * Academic minor, a secondary field of study in undergraduate education Music theory *Minor chord ** Barb ...

can be sent to prison to await trial at the age of 15. * In some countries, it is the legal age for sexual consent.Worldwide Ages of Consent
Avert.org. Retrieved on 2011-11-01. * 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. * The drinking age in

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 in

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 15 puzzle (also called Gem Puzzle, Boss Puzzle, Game of Fifteen, Mystic Square and many others) is a sliding puzzle having 15 square tiles numbered 1–15 in a frame that is 4 tiles high and 4 tiles wide, leaving one unoccupied tile position ...

. * 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