# 20 (number)

 ← 19 20 21 →
Cardinaltwenty
Ordinal20th
(twentieth)
Numeral systemvigesimal
Factorization22 × 5
Divisors1, 2, 4, 5, 10, 20
Greek numeralΚ´
Roman numeralXX
Binary101002
Ternary2023
Senary326
Octal248
Duodecimal1812

20 (twenty; Roman numeral XX) 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

An icosahedron has twenty triangular faces.

Twenty is a pronic number, as it is the product of consecutive integers, namely 4 and 5.[3] It is the third composite number to be the product of a squared prime and a prime, and also the second member of the (22)q family in this form.

• 20 is the number of parallelogram polyominoes with 5 cells.[7]
• 20 is the number of moves (quarter or half turns) required to optimally solve a Rubik's Cube in the worst case.[8][9]

There are twenty edge-to-edge 2-uniform tilings by convex regular polygons, which are uniform tessellations of the plane containing 2 orbits of vertices.[10][11]

The largest number of faces a Platonic solid can have is twenty faces, which make up a regular icosahedron.[12] A dodecahedron, on the other hand, has twenty vertices, likewise the most a regular polyhedron can have.[13]

There are four uniform compound polyhedra that contain twenty polyhedra (UC13, UC14, UC19, UC33), the most any such solids can have, while another twenty compounds contain five polyhedra. The compound of twenty octahedra can be obtained by orienting two pairs of compounds of ten octahedra, which can also coincide to yield a regular compound of five octahedra.

Bring's curve is a Riemann surface of genus four, whose fundamental polygon is a regular hyperbolic 20-sided icosagon, with an area equal to ${\displaystyle 12\pi }$ by the Gauss-Bonnet theorem.[14]

There are twenty semiregular polytopes, inclusive of the 13 Archimedean solids, and 7 Gosset polytopes that exist up through the eighth dimension. These, without counting chiral forms of the snub cube and snub dodecahedron, or the infinite family of semiregular prisms and antiprisms that exists in the third dimension.

The Happy Family of sporadic groups is made up of twenty finite simple groups that are all subquotients of the friendly giant, the largest sporadic group. The largest supersingular prime factor that divides the order of the friendly giant is 71, which is the 20th indexed prime number.

## In science

### 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".[15]

## 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),[16] but also often used as an indefinite number[17] (e.g. the newspaper headline "Scores of Typhoon Survivors Flown to Manila").[18]

## In sports

A standard dartboard is laid out as 20 sectors.

## Music

Albums
20 Related Twenty Related
Harry Connick, Jr.[27] 20+ Baron Rojo[28] Bob Baldwin[29] Twenty+ All-4-One[30]
Orbital[31] 20% Maria Bamford[32] Boyz II Men[33] 20 [Twenty] FT Island[34]
TLC[35] Chicane[36]
Jars of Clay[37] Robert Cray[38]
Africa Unite[39] Jebediah[40]
Kate Rusby[41] Lynyrd Skynyrd[42]
Hyukoh[43] Taking Back Sunday[44]
Pastora Soler[45]
Sofa Surfers[47]
Capo Plaza[48]
John Dahlbäck[49]
Songs
20 Related Twenty
Ebbo Kraan[50] #20 - Fat Tuesday[51] The Rippingtons[52]
Seventeen[53] #20 - Aphex Twin[54]
Janet Jackson[55] #20 - Tony Wilson Sextet[56]
Gorky's Zygotic Mynci[57] #20 - David Paul Mesler[58]
Covenant[59] $20 - Low (band)[60] Car 44[61]$20 - Qwiksand[62]
Karma to Burn[63] $20 - Norman Palm[64] Ike Yard[65] 20% - Furyus[66] Noah Stone[67] 20% - Banfi[68] Alec Empire[69] -20 - Brendon Moeller[70] Beans[71] -20 - Mr. 76ix[72] Damián Schwartz[73] 20 (intro) - Janet Jackson[74] Anarchestra[75] 20 (Palbarrio) - El Barrio[76] ## In other fields ## See also ## References 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. ^ "score | Origin and meaning of score by Online Etymology Dictionary". www.etymonline.com. Retrieved 2020-08-16. 3. ^ "Sloane's A002378: Pronic numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2020-11-30. 4. ^ "Sloane's A071395 : Primitive abundant numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31. 5. ^ "Sloane's A000292 : Tetrahedral numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31. 6. ^ Weisstein, Eric W. "Vigesimal". mathworld.wolfram.com. Retrieved 2020-08-16. 7. ^ 8. ^ "God's Number is 20". Cube20.org 9. ^ Jonathan Fildes (August 11, 2010). "Rubik's Cube quest for speedy solution comes to an end". BBC News. 10. ^ Grünbaum, Branko; Shephard, Geoffrey C. (1977). "Tilings by regular polygons" (PDF). Mathematics Magazine. 50 (5): 235. doi:10.2307/2689529. JSTOR 2689529. S2CID 123776612. Zbl 0385.51006. 11. ^ Sloane, N. J. A. (ed.). "Sequence A068599 (Number of n-uniform tilings.)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2023-01-07. 12. ^ Weisstein, Eric W. "Icosahedron". mathworld.wolfram.com. Retrieved 2020-08-16. 13. ^ Weisstein, Eric W. "Dodecahedron". mathworld.wolfram.com. Retrieved 2020-08-16. 14. ^ 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. 15. ^ "Definition of 20/20". www.merriam-webster.com. Retrieved 2020-08-16. 16. ^ "Definition of SCORE". www.merriam-webster.com. Retrieved 2020-08-16. 17. ^ "Biblical Criticism", The Classical Journal 36:71:83ff (March 1827) full text 18. ^ "CBS News", Scores of Typhoon Survivors Flown to Manila (November 2013) 19. ^ Cleaver, Dylan (2010-11-03). Brendon McCullum: Inside Twenty20. Hachette New Zealand. ISBN 978-1-86971-238-9. 20. ^ 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 ... 21. ^ 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 22. ^ 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 23. ^ Harari, P. J.; Ominsky, Dave (2002). Basketball Made Simple: A Spectator's Guide. First Base Sports, Inc. p. 58. ISBN 978-1-884309-13-7. Duration two 20-min. halves 24. ^ "International Ice Hockey Federation - Olympic Sport". International Olympic Committee. 9 November 2020. Retrieved 22 January 2021. 25. ^ "Adulthood | Introduction to Psychology". lumenlearning.com. 26. ^ "Japan's Age of Majority Changed to 18 - Living the Japon.com". www.japan-experience.com. Retrieved 19 March 2018. 27. ^ 20 - Harry Connick, Jr. | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 28. ^ 20+ - Baron Rojo | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 29. ^ Twenty - Bob Baldwin | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 30. ^ Twenty + - All-4-One | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-17 31. ^ 20 - Orbital | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 32. ^ 20 - Harry Connick, Jr. | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 33. ^ Twenty - Boyz II Men | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 34. ^ 20 (Twenty) - FT Island | User Reviews | AllMusic, retrieved 2020-08-17 35. ^ 20 - TLC | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 36. ^ Twenty - Chicane | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-17 37. ^ 20 - Jars of Clay | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 38. ^ Twenty - Robert Cray | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 39. ^ 20 - Africa Unite | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 40. ^ Twenty - Jebediah | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-17 41. ^ 20 - Kate Rusby | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 42. ^ Twenty - Lynyrd Skynyrd | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 43. ^ 20 - Hyukoh | User Reviews | AllMusic, retrieved 2020-08-16 44. ^ Twenty - Taking Back Sunday | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 45. ^ 20 - Pastora Soler | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 46. ^ 20 - The Gift | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-16 47. ^ 20 - Sofa Surfers | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-17 48. ^ 20 - Capo Plaza | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-17 49. ^ 20 - John Dahlbäck | Songs, Reviews, Credits | AllMusic, retrieved 2020-08-17 50. ^ 20 - Ebbo Kraan | Song Info | AllMusic, retrieved 2020-08-17 51. ^ #20 - Fat Tuesday | Song Info | AllMusic, retrieved 2020-08-17 52. ^ Twenty - The Rippingtons | Song Info | AllMusic, retrieved 2020-08-17 53. ^ 20 - Seventeen | Song Info | AllMusic, retrieved 2020-08-17 54. ^ #20 - Aphex Twin | Song Info | AllMusic, retrieved 2020-08-17 55. ^ 20 - Janet Jackson | Song Info | AllMusic, retrieved 2020-08-17 56. ^ #20 - Tony Wilson Sextet | Song Info | AllMusic, retrieved 2020-08-17 57. ^ 20 - Gorky's Zygotic Mynci | Song Info | AllMusic, retrieved 2020-08-17 58. ^ # 20 - David Paul Mesler | Song Info | AllMusic, retrieved 2020-08-17 59. ^ 20 - Covenant | Song Info | AllMusic, retrieved 2020-08-17 60. ^$20 - Low | Song Info | AllMusic, retrieved 2020-08-17
61. ^ 20 - Car 44 | Song Info | AllMusic, retrieved 2020-08-17
62. ^ $20 - Qwiksand | Song Info | AllMusic, retrieved 2020-08-17 63. ^ 20 - Karma to Burn | Song Info | AllMusic, retrieved 2020-08-17 64. ^$20 - Norman Palm | Song Info | AllMusic, retrieved 2020-08-17
65. ^ 20 - Ike Yard | Song Info | AllMusic, retrieved 2020-08-17
66. ^ 20% - Furyus | Song Info | AllMusic, retrieved 2020-08-17
67. ^ 20 - Noah Stone | Song Info | AllMusic, retrieved 2020-08-17
68. ^ 20% - Banfi | Song Info | AllMusic, retrieved 2020-08-17
69. ^ 20 - Alec Empire | Song Info | AllMusic, retrieved 2020-08-17
70. ^ -20 - Brendon Moeller | Song Info | AllMusic, retrieved 2020-08-17
71. ^ 20 - Beans | Song Info | AllMusic, retrieved 2020-08-17
72. ^ -20 - Mr. 76ix | Song Info | AllMusic, retrieved 2020-08-17
73. ^ 20 - Damián Schwartz | Song Info | AllMusic, retrieved 2020-08-17
74. ^ 20 (Intro) - Janet Jackson | Song Info | AllMusic, retrieved 2020-08-17
75. ^ 20 - Anarchestra | Song Info | AllMusic, retrieved 2020-08-17
76. ^ 20 (Palbarrio) - El Barrio | Song Info | AllMusic, retrieved 2020-08-17
77. ^ "international phone country calling codes". www.globaltel.com. Retrieved 2020-08-16.
78. ^ "CB Slang: Ten Codes". www.cbslang.com. Retrieved 2020-08-16.
79. ^ "Welcome to the Online Browsing Platform (OBP)". www.iso.org. Retrieved 2020-08-16.
80. ^ "Topical Bible: Kaph". biblehub.com. Retrieved 2020-08-17.
81. ^ Toone, Matthew (2009). Great Games!: 175 Games and Activities for Families, Groups and Children. Great Games Book. p. 145. ISBN 978-0-9798345-5-4. Much like the classic game of 20 Questions,...