'20' ('twenty') is the
natural number following
19 and preceding
21. A group of twenty units is often referred to as a 'score'.
In mathematics
Twenty is a
composite number, its proper
divisors being
1,
2,
4,
5 and
10. 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 the second positive integer with a prime factorization of the form
, where ''q'' is a prime. Its
aliquot sum is 22, and its
aliquot sequence is (20,22,14,10,8,7,1,0).
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.
In science
★ The
atomic number of
calcium.
★ The third
Magic number (physics).
Biology
★ The number of
proteinogenic amino acids that are encoded by the standard genetic code.
★ 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 religion
Age 20 is the age at which
Levites in the time of
King David were allowed "to do the work for the service of the house of the Lord", the
Temple in Jerusalem (see
First Chronicles Chapter 24, verses 24 and 27). In the time of
Ezra and
Nehemiah, following the
Babylonian captivity, it was
Levites from the age of 20 upwards who were assigned "to oversee the work of the house of the LORD" (
Ezra Chapter 3, verse 8.
In sports
★ 20 is the retired number of
Pro Football Hall of Fame running back
Barry Sanders, formerly of the
Detroit Lions.
★ The retired number of former baseball stars
Frank Robinson,
Mike Schmidt,
Mark Fidrych and
Lou Brock.
★ 20 is the number of
Tony Stewart's 2-time winning
NASCAR NEXTEL Cup Series car.
★ The
Twenty20 Cup is a form of limited Overs
Cricket where each team plays only 20
Overs.
★ The number of
NFL stars
Ed Reed,
Ronde Barber and
Brian Dawkins.
★ 20 is the number worn by
NBA player
Manu Ginobili of the
San Antonio Spurs.
★ 20 is the iconic number worn by
Football player
Ole Gunnar Solskjaer of
Manchester United.
★ 20 is the number worn by
New York Yankees catcher
Jorge Posada.
★ A twenty-game winner (
pitcher) in
baseball is acclaimed as having reached a milestone in a season. The most remarkable of 20-game winners was probably
Hank Borowy, who won 10 games with the
Yankees in
1945 before being put on
waivers, then signed with the
Cubs and won 11 more games playing the rest of the season. He had been in the
World Series with the Yanks and played for Chicago in the '45 Series as well.
★ 20 was the number Fred Jones wore when he played college basketball for the University of Oregon. He also wore it when he played for the NBA teams, the Indiana Pacers; and the Toronto Raptors before switching to the number 0 when he was traded to the Portland Trailblazers
★ Lukas Podolski, German National soccer player, wears number 20.
★ 20 is the new jersey number worn by
Ray Allen.
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 20 first moves from which to choose
★
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 assumed 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 and
20goto10.
★ 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, 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.
'20' is:
★ '
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
★
CB radio jargon 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
Historical years
'20 A.D.',
20 B.C.,
1920,
2020, etc.
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