15 (number)

Mathematics

• a lucky number.
• a triangular number.
• a hexagonal number.
• a pentatope number.
• the 5th Bell number.
• a composite number; its proper divisors being, and.
• the number of supersingular primes.
• a repdigit in binary and quaternary. In hexadecimal, as well as all higher bases, 15 is represented as F.
• the smallest number that can be factorized using Shor's quantum algorithm.
• the magic constant of the unique order-3 normal magic square:

Science

• The atomic number of phosphorus.
• Group 15 of the periodic table are sometimes known as the pnictogens.

  Religion

Sunnism

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", because those spell out one of the Jewish names of God. Instead, the date is written with the letters representing "9" and "6"
• Passover begins on the 15th day of the Hebrew month of Nisan
• Sukkot begins on the 15th day of the Hebrew month of Tishrei
• Tu Bishvat is a Jewish holiday occurring on the 15th of the Hebrew month of Shevat

  Modern use

Sports

• In all four of the major Gaelic games—hurling, Gaelic football for men and women, and camogie—each team has 15 players on the field at any given time.
• In both major forms of gridiron football, standard games are played in 15-minute quarters.
• In rugby union:
• * Each team has 15 players on the field at any given time.
• * The jersey number 15 is worn by the starting fullback.
• In tennis, the number 15 represents the first point gained in a game.
• In NCAA Division I women's college basketball, teams are allowed to provide scholarships to no more than 15 players at any given time.
• In Australian rules football, games in the AFL Women's league consist of 15-minute quarters.

  Age 15

• The age of a quinceañera, a Latina girl celebrating her 15th birthday. Thus, Spanish bingo callers might refer to the number 15 as la niña bonita.
• The age for obtaining a driver's permit in certain jurisdictions, including some, where the legal age for a driver's license is 16.
• 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 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.
• The drinking age in Ethiopia.
• The age of majority in Indonesia, Myanmar, and Yemen.

  Music

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

  In other fields

• 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.