20 (number)
| ||||
|---|---|---|---|---|
| Cardinal | twenty | |||
| Ordinal | 20th (twentieth) | |||
| Numeral system | vigesimal | |||
| Factorization | 22 × 5 | |||
| Divisors | 1, 2, 4, 5, 10, 20 | |||
| Greek numeral | Κ´ | |||
| Roman numeral | XX, xx | |||
| Binary | 101002 | |||
| Ternary | 2023 | |||
| Senary | 326 | |||
| Octal | 248 | |||
| Duodecimal | 1812 | |||
| Hexadecimal | 1416 | |||
| Armenian | Ի | |||
| Hebrew | כ / ך | |||
| Babylonian numeral | ⟪ | |||
| Egyptian hieroglyph | 𓎏 | |||
20 (twenty) is the natural number following 19 and preceding 21. A group of twenty units is sometimes referred to as a score.[1][2]
In Mathematics
[edit]Twenty is a composite number. It is also the smallest primitive abundant number.[3] The Happy Family of sporadic groups is made up of twenty finite simple groups that are all subquotients of the friendly giant, the largest of twenty-six sporadic groups.
Geometry
[edit]An icosagon is a polygon with 20 edges. Bring's curve is a Riemann surface, whose fundamental polygon is a regular hyperbolic icosagon.[4]
Platonic Solids
[edit]
The largest number of faces a Platonic solid can have is twenty faces, which make up a regular icosahedron.[5] A dodecahedron, on the other hand, has twenty vertices, likewise the most a regular polyhedron can have.[6] This is because the icosahedron and dodecahdron are duals of each other.
Other fields
[edit]Science
[edit]20 is the third magic number in physics.
Biology
[edit]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"[7]
Psycology
In many disciplines of developmental psychology, adulthood starts at age 20.[8]
Culture
[edit]Age 20
[edit]Formerly the age of majority in Japan and in Japanese tradition.[9]
Number systems
[edit]20 is the basis for vigesimal number systems, used by several different civilizations in the past (and to this day), including the Maya.[10]
Indefinite number
[edit]A 'score' is a group of twenty (often used in combination with a cardinal number, e.g. fourscore to mean 80),[11] but also often used as an indefinite number[12] (e.g. the newspaper headline "Scores of Typhoon Survivors Flown to Manila").[13]
References
[edit]- ^ 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 A071395 : Primitive abundant numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
- ^ Weber, Matthias (2005). "Kepler's small stellated dodecahedron as a Riemann surface" (PDF). Pacific Journal of Mathematics. 220 (1): 172. doi:10.2140/pjm.2005.220.167. MR 2195068. S2CID 54518859. Zbl 1100.30036.
- ^ Weisstein, Eric W. "Icosahedron". mathworld.wolfram.com. Retrieved 2020-08-16.
- ^ Weisstein, Eric W. "Dodecahedron". mathworld.wolfram.com. Retrieved 2020-08-16.
- ^ "Definition of 20/20". www.merriam-webster.com. Retrieved 2020-08-16.
- ^ "Adulthood | Introduction to Psychology". lumenlearning.com.
- ^ "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.
- ^ "Definition of SCORE". www.merriam-webster.com. Retrieved 2020-08-16.
- ^ "Biblical Criticism", The Classical Journal 36:71:83ff (March 1827) full text
- ^ "CBS News", Scores of Typhoon Survivors Flown to Manila (November 2013)
External links
[edit]
Media related to 20 (number) at Wikimedia Commons
