21
Cardinal	twenty-one
Ordinal	twenty-first
Factorization
Roman numeral	XXI
Binary	10101
Hexadecimal	15

Mathematics

Twenty-one is a Fibonacci number, a triangular number as well as a composite number, its proper divisors being 1, 3 and 7.

Age 21

Before the Family Law Reform Act of 1969, 21 was the age of majority in England. The act set it so that it would be lowered to 18 at the dawning of January 1, 1970.

In the United States, when one reaches 21, one gains the right to drink alcohol. It is also the age at which it is legal to gamble and have sex with a prostitute in Nevada. In most states, a person who is 21 or over may also rent a car. 21 was the age for voting in the majority of states until the introduction of the Twenty-sixth Amendment.

Other fields

The century that we are in currently is referred as the 21st century. It spans from 2001 to 2100. Inspired by the designation of the first century of the millennium, Century 21 is a large real estate agent.

The Twenty-first Amendment repealed the Eighteenth Amendment, thereby ending Prohibition.

Pier21 was, from 1928 to 1971, the place where immigrants entered Canada. It was called the "Gateway to Canada".

Twenty-one is:

• The atomic number of scandium.
• The number of spots on a die (1+2+3+4+5+6).
• The number of guns in gun salute to the U.S. President and the U.S. flag.
• A card game, also called vingt-et-un or blackjack.
• The title of a TV quiz show that ran from 1956 to 1958, most remembered for the scandal that the wins were fixed. It was remade in 2000.
• The title of at least two different movies: a 1918 comedy starring Bryant Washburn and Gertrude Selby; and a 1923 drama starring Richard Barthelmess and Dorothy Mackaill.
• the standard TCP/IP port number for FTP connection.
• Twenty-One Demands
• Number 21, the plane flown by Gustave Whitehead
• The year AD 21.

List of numbers

19 - 20 - 21 - 22 - 23

Integer