In decimal, 20 is the smallest non-trivial neon number equal to the sum of its digits when raised to the thirteenth power (2013 = 8192 × 1013).[citation needed]
In total, there are 20 semiregular polytopes that only exist up through the 8th dimension, which include 13 Archimedean solids and 7 Gosset polytopes (without counting enantiomorphs, or semiregular prisms and antiprisms).
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" in 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"[22]
20 is the basis for vigesimal number systems, used by several different civilizations in the past (and to this day), including the Maya.[27]
Board gamesedit
In chess, 20 is the number of legal moves for each player in the starting position.[28]
Indefinite numberedit
A 'score' is a group of 20 (often used in combination with a cardinal number, e.g. fourscore to mean 80),[29] but also often used as an indefinite number[30] (e.g. the newspaper headline "Scores of Typhoon Survivors Flown to Manila").[31]
Referencesedit
^This is the second Pythagorean triple that can be formed using Pell numbers where and are one unit apart. The first such triple is the smallest Pythagorean triple, (4,3,5). These can be formed using Pell numbers that yield a Pythagorean triple of the form .
^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,
so "score" also came to mean 20."
^"score | Origin and meaning of score by Online Etymology Dictionary". www.etymonline.com. Retrieved 2020-08-16.
^"Sloane's A002378: Pronic numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2020-11-30.
^"Sloane's A071395 : Primitive abundant numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
^Sloane, N. J. A. (ed.). "Sequence A103606 (Primitive Pythagorean triples in nondecreasing order of perimeter, with each triple in increasing order, and if perimeters coincide then increasing order of the even members.)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2023-07-06.
^"Sloane's A000292 : Tetrahedral numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
^Jonathan Fildes (August 11, 2010). "Rubik's Cube quest for speedy solution comes to an end". BBC News.
^"Adulthood | Introduction to Psychology". lumenlearning.com.
^"Definition of 20/20". www.merriam-webster.com. Retrieved 2020-08-16.
^Draper, Nick (2014-12-05). Exercise Physiology: For Health and Sports Performance. Routledge. p. 404. ISBN 978-1-317-90260-7. played over four 20 min quarters
^"International Ice Hockey Federation - Olympic Sport". International Olympic Committee. 9 November 2020. Retrieved 22 January 2021.
^Ziemba, William T. (2017-08-23). The Adventures Of A Modern Renaissance Academic In Investing And Gambling. World Scientific. p. 352. ISBN 978-981-314-853-6. It has always been for a long time a maximum of 20 horses ...
^"Japan's Age of Majority Changed to 18 - Living the Japon.com". www.japan-experience.com. Retrieved 19 March 2018.
^Weisstein, Eric W. "Vigesimal". mathworld.wolfram.com. Retrieved 2020-08-16.
^Jordan, Bill. Opening Moves Made Easy: A new way to learn how to play Chess openings. Bill Jordan. there are 20 legal moves for White and 20 legal replies for Black
^"Definition of SCORE". www.merriam-webster.com. Retrieved 2020-08-16.
^"Biblical Criticism", The Classical Journal36:71:83ff (March 1827) full text
^"CBS News", Scores of Typhoon Survivors Flown to Manila (November 2013)
External linksedit
Look up twenty in Wiktionary, the free dictionary.