Natural number
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 2 2 × q family in this form.
20 has an
aliquot sum of
22 ; a
semiprime , within an
aliquot sequence of four
composite numbers (20, 22,
14 ,
10 ,
8 ) that belong to the prime
7 -aliquot tree.
20 is the first number to have an
abundance of
2 , followed by
104 .
[11]
Gelfond's constant and
pi
very nearly have a difference equal to twenty:
e
π
−
π
≈
20
{\displaystyle e^{\pi }-\pi \;\approx \;20}
differing only by about
−
0.000900020811
…
{\displaystyle -0.000900020811\ldots }
from an
integer value.
[12]
[13]
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 .
[14]
[15]
The largest number of faces a
Platonic solid can have is twenty faces, which make up a regular
icosahedron .
[16] A
dodecahedron , on the other hand, has twenty vertices, likewise the most a regular polyhedron can have.
[17] There are a total of 20
regular and
semiregular polyhedra, aside from the infinite family of semiregular
prisms and
antiprisms that exists in the third dimension: the 5 Platonic solids, and 15
Archimedean solids (including
chiral forms of the
snub cube and
snub dodecahedron ). There are also four
uniform compound polyhedra that contain twenty polyhedra (
UC13 ,
UC14 ,
UC19 ,
UC33 ), which is the most any such solids can have; while another twenty uniform compounds contain five polyhedra (that are not part of classes of infinite families, where there exist three more). 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 .
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).
Bring's curve is a
Riemann surface of
genus four, whose
fundamental polygon is a regular hyperbolic twenty-sided
icosagon , with an area equal to
12
π
{\displaystyle 12\pi }
by the
Gauss-Bonnet theorem .
[18]
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. The largest
supersingular prime factor that divides the order of the friendly giant is
71 , which is the 20th
indexed prime number, where 26 also represents the number of
partitions of 20 into prime parts.
[19] Both 71 and 20 represent
self-convolved Fibonacci numbers, respectively the seventh and fifth members
j
{\displaystyle j}
in this sequence
F
j
2
{\displaystyle F_{j}^{2}}
.
[20]
[21]
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" 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]
As an indefinite number
A 'score' is a group of 20 (often used in combination with a
cardinal number , e.g. fourscore to mean 80),
[23] but also often used as an
indefinite number
[24] (e.g. the newspaper headline "Scores of Typhoon Survivors Flown to Manila").
[25]
In sports
A standard
dartboard is laid out as 20
sectors .
Age 20
Music
In other fields
See also
References
^ 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
(
2
P
n
P
n
+
1
,
P
n
+
1
2
−
P
n
2
,
P
n
+
1
2
+
P
n
2
=
P
2
n
+
1
)
{\displaystyle \left(2P_{n}P_{n+1},P_{n+1}^{2}-P_{n}^{2},P_{n+1}^{2}+P_{n}^{2}=P_{2n+1}\right)}
.
^ 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's A000292 : Tetrahedral numbers" . The On-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved 2016-05-31 .
^ Weisstein, Eric W.
"Vigesimal" . mathworld.wolfram.com . Retrieved 2020-08-16 .
^
Sloane, N. J. A. (ed.).
"Sequence A006958 (Number of parallelogram polyominoes with n cells (also called staircase polyominoes, although that term is overused))" . The
On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
^
"God's Number is 20" . Cube20.org
^ Jonathan Fildes (August 11, 2010).
"Rubik's Cube quest for speedy solution comes to an end" .
BBC News .
^
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, N. J. A. (ed.).
"Sequence A088831 (Numbers k whose abundance is 2: sigma(k) - 2k is 2.)" . The
On-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved 2024-01-23 .
^ Maze, Gérard; Minder, Lorenz (2007).
"A new family of almost identities" .
Elemente der Mathematik . 62 (3). Hensinki:
European Mathematical Society : 90.
arXiv :
math/0409014 .
doi :
10.4171/EM/61 .
MR
2350250 .
S2CID
56024534 .
Zbl
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^
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"Sequence A018938 (Decimal expansion of e^Pi - Pi.)" . The
On-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved 2023-12-09 .
^ Grünbaum, Branko; Shephard, Geoffrey C. (1977).
"Tilings by regular polygons" (PDF) .
Mathematics Magazine . 50 (5): 235.
doi :
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JSTOR
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S2CID
123776612 .
Zbl
0385.51006 .
^
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 .
^ Weisstein, Eric W.
"Icosahedron" . mathworld.wolfram.com . Retrieved 2020-08-16 .
^ Weisstein, Eric W.
"Dodecahedron" . mathworld.wolfram.com . Retrieved 2020-08-16 .
^ 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 .
^
Sloane, N. J. A. (ed.).
"Sequence A000607 (Number of partitions of n into prime parts.)" . The
On-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved 2024-03-24 .
^
Sloane, N. J. A. (ed.).
"Sequence A001629 (Self-convolution of Fibonacci numbers.)" . The
On-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved 2023-07-16 .
^ Moree, Pieter (2004).
"Convoluted Convolved Fibonacci Numbers" (PDF) .
Journal of Integer Sequences . 7 (2). Waterloo, Ont., CA:
University of Waterloo
David R. Cheriton School of Computer Science : 13 (Article 04.2.2).
arXiv :
math.CO/0311205 .
Bibcode :
2004JIntS...7...22M .
MR
2084694 .
S2CID
14126332 .
Zbl
1069.11004 .
^
"Definition of 20/20" . www.merriam-webster.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)
^ Cleaver, Dylan (2010-11-03).
Brendon McCullum: Inside Twenty20 . Hachette New Zealand.
ISBN
978-1-86971-238-9 .
^ 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 ...
^ 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
^ 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
^ 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
^
"International Ice Hockey Federation - Olympic Sport" . International Olympic Committee . 9 November 2020. Retrieved 22 January 2021 .
^
"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 .
^
20 - Harry Connick, Jr. | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
20+ - Baron Rojo | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
Twenty - Bob Baldwin | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
Twenty + - All-4-One | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-17
^
20 - Orbital | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
20 - Harry Connick, Jr. | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
Twenty - Boyz II Men | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
20 (Twenty) - FT Island | User Reviews | AllMusic , retrieved 2020-08-17
^
20 - TLC | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
Twenty - Chicane | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-17
^
20 - Jars of Clay | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
Twenty - Robert Cray | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
20 - Africa Unite | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
Twenty - Jebediah | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-17
^
20 - Kate Rusby | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
Twenty - Lynyrd Skynyrd | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
20 - Hyukoh | User Reviews | AllMusic , retrieved 2020-08-16
^
Twenty - Taking Back Sunday | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
20 - Pastora Soler | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
20 - The Gift | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-16
^
20 - Sofa Surfers | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-17
^
20 - Capo Plaza | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-17
^
20 - John Dahlbäck | Songs, Reviews, Credits | AllMusic , retrieved 2020-08-17
^
20 - Ebbo Kraan | Song Info | AllMusic , retrieved 2020-08-17
^
#20 - Fat Tuesday | Song Info | AllMusic , retrieved 2020-08-17
^
Twenty - The Rippingtons | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Seventeen | Song Info | AllMusic , retrieved 2020-08-17
^
#20 - Aphex Twin | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Janet Jackson | Song Info | AllMusic , retrieved 2020-08-17
^
#20 - Tony Wilson Sextet | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Gorky's Zygotic Mynci | Song Info | AllMusic , retrieved 2020-08-17
^
# 20 - David Paul Mesler | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Covenant | Song Info | AllMusic , retrieved 2020-08-17
^
$20 - Low | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Car 44 | Song Info | AllMusic , retrieved 2020-08-17
^
$20 - Qwiksand | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Karma to Burn | Song Info | AllMusic , retrieved 2020-08-17
^
$20 - Norman Palm | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Ike Yard | Song Info | AllMusic , retrieved 2020-08-17
^
20% - Furyus | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Noah Stone | Song Info | AllMusic , retrieved 2020-08-17
^
20% - Banfi | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Alec Empire | Song Info | AllMusic , retrieved 2020-08-17
^
-20 - Brendon Moeller | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Beans | Song Info | AllMusic , retrieved 2020-08-17
^
-20 - Mr. 76ix | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Damián Schwartz | Song Info | AllMusic , retrieved 2020-08-17
^
20 (Intro) - Janet Jackson | Song Info | AllMusic , retrieved 2020-08-17
^
20 - Anarchestra | Song Info | AllMusic , retrieved 2020-08-17
^
20 (Palbarrio) - El Barrio | Song Info | AllMusic , retrieved 2020-08-17
^
"international phone country calling codes" . www.globaltel.com . Retrieved 2020-08-16 .
^
"CB Slang: Ten Codes" . www.cbslang.com . Retrieved 2020-08-16 .
^
"Welcome to the Online Browsing Platform (OBP)" . www.iso.org . Retrieved 2020-08-16 .
^
"Topical Bible: Kaph" . biblehub.com . Retrieved 2020-08-17 .
^ 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,...
External links
Look up
twenty in Wiktionary, the free dictionary.
100,000
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