20 (number)
20 (twenty) is the natural number following 19 and preceding 21. A group of twenty units may
also be referred to as a score.
[1]
In mathematics
An icosahedron has 20 faces
20 is a tetrahedral number as 1, 4, 10, 20.
20 is the basis for vigesimal number systems.
20 is the third composite number comprising the product of a squared prime and a prime,
and also the second member of the (2
2
)q family in this form.
20 has an aliquot sum of 22 (110% in abundance). Accordingly, 20 is the third abundant
number and demonstrates an 8 member aliquot sequence; {20, 22, 14, 10, 8, 7, 1, 0}.
20 is the smallest primitive abundant number.
20 is the 4th composite number in the 7-aliquot tree. Two numbers have 20 as their
aliquot sum; the discrete semiprime 34 and the squared prime 361. Only 2 other square
primes are abundant 12 and 18.
An icosahedron has 20 faces. A dodecahedron has 20 vertices.
20 can be written as the sum of three Fibonacci numbers uniquely, i.e. 20 = 13 + 5 + 2.
The product of the number of divisors and the number of proper divisors of 20 is exactly
20.
20 is the number of quarter or half turns required to optimally solve a Rubik's Cube in the
worst case.
20 is the only number with more than one digit that can be written from base 2 to base 20
using only the digits 0 to 9.
[2]
In science
The atomic number of calcium.
The third magic number in physics.
The IAU shower number for Coma Berenicids.
Biology
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".
As an indefinite number
A 'score' is a group of 20 (often used in combination with a cardinal number, i.e.
fourscore to mean 80), but also often used as an indefinite number
[3]
(i.e. the newspaper
headline "Scores of Typhoon Survivors Flown to Manila")
[4]
In sports
A standard dartboard is laid out as 20 sectors
The jersey number 20 has been retired by several North American sports teams in honor
of past playing greats:
o In Major League Baseball:
The Arizona Diamondbacks, for Luis Gonzalez.
The Baltimore Orioles and Cincinnati Reds, both for Hall of Famer Frank
Robinson.
The Kansas City Royals, for Frank White.
The Los Angeles Dodgers, for Hall of Famer Don Sutton.
The Philadelphia Phillies, for Hall of Famer Mike Schmidt.
The Pittsburgh Pirates, for Hall of Famer Pie Traynor.
The St. Louis Cardinals, for Hall of Famer Lou Brock.
The San Francisco Giants, for Hall of Famer Monte Irvin, who played for
the team when it was the New York Giants.
o In the NFL:
The Detroit Lions, for Hall of Famer Barry Sanders.
The New England Patriots, for Gino Cappelletti, who played for the team
when it was known by its original name of the Boston Patriots.
The Philadelphia Eagles, for Brian Dawkins.
o In the NBA:
The Portland Trail Blazers, for Maurice Lucas.
o In the NHL:
The Los Angeles Kings, for Hall of Famer Luc Robitaille.
The Kentucky Derby currently has a maximum field of 20 horses.
In the NASCAR Sprint Cup Series, car #20 is currently owned by Joe Gibbs Racing.
Tony Stewart won the Cup Series title twice in the #20 car while with Joe Gibbs Racing.
After Stewart left the team in 2009 to drive for himself in the StewartHaas Racing
team, rookie Joey Logano took over the car until the end of the 2012 season to drive for
Penske Racing. The #20 car is now being driven by Matt Kenseth, who left Roush-
Fenway Racing at the end of the 2012 season.
Twenty20 is a form of limited overs cricket where each team plays only 20 overs.
In rugby union, 20 national teams currently qualify for each edition of the Rugby World
Cup.
Age 20
