- "Twenty" redirects here. For the village in England, see Twenty, Lincolnshire.
) is the natural number
and preceding 21
. A group of twenty units may also be referred to as a score
Twenty is a composite number
, its proper divisors
. Skipping 2 and adding the other divisors gives 20, hence 20 is a semiperfect number
, and since it is not divisible by any of the smaller semiperfect numbers, it is a primitive semiperfect number
. 20 is the smallest abundant number
that is not a multiple of 3.20 is also a composite number.
20 is the second positive integer with a prime factorization of the form where q is a prime. Twenty is the third number in abundance (110%) with the aliquot sum of 22 within the 8-member aliquot sequence (20,22,14,10,8,7,1,0). Twenty is the aliquot sum of the discrete biprime, 34 and the square 361.
It is also the sum of the first four triangular numbers, making it a tetrahedral number.
20 is the total number of digits on the human body, which makes it a convenient number system radix; such number systems are called vigesimal. In the former British currency system, there were twenty shillings in a pound.
A polyhedron with twenty faces is an icosahedron.
Twenty is the first number in an early Indian magic square of order 3.
In base 10, it is a Harshad number and the smallest even self number.
The Monster group contains 20 sporadic groups.
- The number of proteinogenic amino acids that are encoded by the standard genetic code.
- In some countries, the number 20 is used as an index in measuring visual acuity. 20/20 indicates normal vision at 20 feet, although it is commonly used to mean "perfect vision" (Note that this applies only to countries using the Imperial system. The metric equivalent is 6/6). When someone is able to see only after an event how things turned out, that person is often said to have had "20/20 hindsight".
- There are 20 baby teeth in the deciduous dentition.
In other fields
- The number of twenty can also be called a score (as Abraham Lincoln did in his Gettysburg Address).
- In a game of chess both players have from which to choose 20 first moves
- Twenty questions is a popular party game
- Twenty is the age of majority in Japanese tradition. Someone who is exactly twenty years old is described as hatachi
- The Twenty Year Curse refers to the pattern of presidents of the United States who were elected to office in 1840, 1860, 1880, 1900, 1920, 1940, and 1960 to die in office. This pattern ended with the 1980 presidency of Reagan, who survived his time in office and, notably, an attempted assassination.
- Bands with the number twenty in their name include Matchbox Twenty
- A 20-minute-long entertainment program shown before some films playing in United Artists movie theaters is called "The Twenty" (spelled "The 20wenty")
- Yan Tan Tethera is a 20-word jingle for counting sheep
- The ordinal adjective is vicenary
- 20/20 is a late-night newsmagazine program on the ABC network, that has been hosted by Barbara Walters, Hugh Downs, Elizabeth Vargas, and others
- In the roleplaying game Dungeons and Dragons (as well as other RPGs that use twenty-sided dice), twenty-sided dice play a pivotal role in gameplay, and to "roll a twenty" is significant to the point that it is sometimes used in other, usually related, contexts, similar to the use of "doubles" in reference to Monopoly.
- Cigarettes are usually packaged with 20 in each pack.
- Twenty, a village in Lincolnshire
- In the United States Constitution, $20 is the threshold value of civil disputes above which the right to trial by jury is preserved
- A denomination of U.S. dollar featuring Andrew Jackson's portrait
- A denomination of Pound sterling featuring Adam Smith's portrait
- The code for international direct dial phone calls to Egypt
- The designation of Interstate 20, a freeway that runs from Texas to South Carolina
- 20 (album), a 1988 album by Harry Connick, Jr.
- Twenty (album), a 1997 album by Lynyrd Skynyrd
- 20 (Terminaator album), a 2007 album by Terminaator
- Twenty (concert), a 2006 concert celebrating the 20th Anniversary of Regine Velasquez held at the Araneta Coliseum, Philippines. It was awarded Best Major Concert Act by the Aliw Awards.
- CB slang for "a place", being short for "10-20", used in reference to a person or object's location
- One of the TCP/IP ports used for File Transfer Protocol
, 20 B.C.