20 (number)

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← 19 20 21 →
Numeral systemvigesimal
Factorization22 × 5
Divisors1, 2, 4, 5, 10, 20
Greek numeralΚ´
Roman numeralXX
Base 36K36

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][2]

In mathematics[edit]

An icosahedron has 20 faces

In science[edit]


  • 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[edit]

  • 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[7] (e.g. the newspaper headline "Scores of Typhoon Survivors Flown to Manila")[8]

In sports[edit]

A standard dartboard is laid out as 20 sectors

Age 20[edit]

In other fields[edit]

See also[edit]


  1. ^ John H. Conway and Richard K. Guy, The Book of Numbers. New York: Copernicus (1996): 11. ""Score" is related to "share" and comes from the Old Norse "skor" meaning a "notch" or "tally" on a stick used for counting. ... Often people counted in 20s; every 20th notch was larger, and so "score" also came to mean 20."
  2. ^ [1]
  3. ^ "Sloane's A000292 : Tetrahedral numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
  4. ^ "Sloane's A071395 : Primitive abundant numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
  5. ^ "God's Number is 20". Cube20.org
  6. ^ Jonathan Fildes (August 11, 2010). "Rubik's Cube quest for speedy solution comes to an end". BBC News.
  7. ^ "Biblical Criticism", The Classical Journal 36:71:83ff (March 1827) full text
  8. ^ "CBS News", Scores of Typhoon Survivors Flown to Manila (November 2013) [2]
  9. ^ "Adulthood | Introduction to Psychology". lumenlearning.com.
  10. ^ "Japan's Age of Majority Changed to 18 - Living the Japon.com". www.japan-experience.com. Retrieved 19 March 2018.