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21 (number)
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21 (number)

21 (twenty-one) is the natural number following 20 and preceding 22.

List of numbersIntegers
<< 20 21 22 23 24 25 26 27 28 29 >>
Cardinal twenty-one
Ordinaltwenty-first
Factorization
Roman numeralXXI
Binary10101
Hexadecimal15

In mathematics

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

In human affairs: age 21

21 had been the age of majority in England and Wales before that age was lowered to 18 with the coming into force, on 1 January 1970, of the Family Law Reform Act 1969.

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.

In other fields

The current century -- spanning the years from 2001 to 2100 -- is referred to as the 21st century. This inspired many forward-looking 20th century event, company, and product names, like the Century 21 Exposition (another name for the 1962 Seattle World's Fair) and Century 21 Real Estate.

The Twenty-first Amendment repealed the Eighteenth Amendment, thereby ending Prohibition.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