View source for 2

{{Short description|Integer number 2}}
{{Hatnote|This article is about the number. For the years, see [[2 BC]] and [[AD 2]]. For other uses, see [[2 (disambiguation)]], [[II (disambiguation)]], and [[Number Two (disambiguation)]].}}
{{pp-vandalism|small=yes}}
{{Infobox number
|number=2
|ordinal=2nd (second)
|numeral=[[binary numeral system|binary]]
|gaussian integer factorization = <math>(1 + i)(1 - i)</math>
|prime=1st
|divisor=1, 2
|roman =II, ii
|greek prefix=[[Wiktionary:di-|di-]]
|latin prefix=[[Wiktionary:duo-|duo-]]/[[Wiktionary:bi-|bi-]]
|old english prefix=[[Wiktionary:twi-|twi-]]
|lang1=[[Greek numeral]]
|lang1 symbol=β'
|lang2=[[Eastern Arabic numerals|Arabic]], [[Central Kurdish|Kurdish]], [[Persian language|Persian]], [[Sindhi language|Sindhi]], [[Urdu numerals|Urdu]]
|lang2 symbol={{resize|150%|٢}}
|lang3=[[Ge'ez alphabet|Ge'ez]]
|lang3 symbol=፪
|lang4=[[Bengali numerals|Bengali]]
|lang4 symbol={{resize|150%|২}}
|lang5=[[Chinese numeral]]
|lang5 symbol=二，弍，貳
|lang6=[[Devanāgarī]]
|lang6 symbol={{resize|150%|२}}
|lang7=[[Santali language|Santali]]
|lang7 symbol={{resize|150%|᱒}}
|lang8=[[Indian numerals#Telugu numerals and their names|Telugu]]
|lang9=[[Tamil numerals|Tamil]]
|lang9 symbol={{resize|150%|௨}}
|lang10=[[Kannada numerals|Kannada]]
|lang10 symbol={{resize|150%|೨}}
|lang11=[[Hebrew numerals|Hebrew]]
|lang11 symbol={{resize|150%|ב}}
|lang12=[[Armenian numerals|Armenian]]|lang12 symbol=Բ|lang13=[[Khmer numerals|Khmer]]
|lang13 symbol=២
|lang14=[[Maya numerals]]|lang14 symbol=••|lang15=[[Thai numerals|Thai]]
|lang15 symbol=๒
|lang16=[[Georgian numerals|Georgian]]	
|lang16 symbol={{resize|130%| Ⴁ/ⴁ/ბ}}([[Bani (letter)|Bani]])
|lang17=[[Malayalam numerals|Malayalam]]
|lang17 symbol=൨
|lang18=[[Babylonian cuneiform numerals|Babylonian numeral]]|lang18 symbol=𒐖|lang19=[[Egyptian numerals|Egyptian hieroglyph]], [[Aegean numerals|Aegean numeral]], [[counting rods|Chinese counting rod]]|lang19 symbol={{!}}{{!}}|lang20=[[Morse code]]|lang20 symbol={{resize|150%|.._ _ _}}}}

'''2''' ('''two''') is a [[number]], [[numeral (linguistics)|numeral]] and [[numerical digit|digit]]. It is the [[natural number]] following [[1]] and preceding [[3]]. It is the smallest and the only even [[prime number]].

Because it forms the basis of a [[Dualistic cosmology|duality]], it has [[Religion|religious]] and [[Spirituality|spiritual]] significance in many [[Culture|cultures]].

== Mathematics ==
The number 2 is the second natural number after [[1]]. Each natural number, including 2, is constructed by succession, that is, by adding 1 to the previous natural number.<ref>{{cite book| last1=Colman| first1=Samuel| editor-last=Coan| editor-first=C. Arthur| title=''Nature's Harmonic Unity: A Treatise on Its Relation to Proportional Form''| publisher=G.P. Putnam's Sons| location=New York and London| year=1912| url=https://archive.org/details/naturesharmonic00coangoog/page/n26/mode/2up|page=10}}</ref> 2 is the smallest and the only even [[prime number]], and the first [[Ramanujan prime]].<ref>{{Cite web |title=Sloane's A104272 : Ramanujan primes |url=https://oeis.org/A104272 |url-status=dead |archive-url=https://web.archive.org/web/20110428165633/https://oeis.org/A104272 |archive-date=2011-04-28 |access-date=2016-06-01 |website=The On-Line Encyclopedia of Integer Sequences |publisher=OEIS Foundation}}</ref> It is also the first [[superior highly composite number]],<ref>{{Cite web |title=A002201 - OEIS |url=https://oeis.org/A002201 |access-date=2024-11-28 |website=oeis.org}}</ref> and the first [[colossally abundant number]].<ref>{{Cite web |title=A004490 - OEIS |url=https://oeis.org/A004490 |access-date=2024-11-28 |website=oeis.org}}</ref>

An [[integer]] is determined to be [[Parity (mathematics)|even]] if it is [[Division (mathematics)|divisible]] by two. When written in base 10, all [[Multiple (mathematics)|multiples]] of 2 will end in [[0]], 2, 4, 6, or [[8]];<ref>{{Cite OEIS|A005843|The nonnegative even numbers|access-date=2022-12-15}}</ref> more generally, in any even base, even numbers will end with an even digit.

A [[digon]] is a polygon with two sides (or [[Edge (geometry)|edges]]) and two [[Vertex (geometry)|vertices]].<ref name="Wilson2014">{{cite book |last=Wilson |first=Robin |title=Four Colors Suffice |publisher=Princeton University Press |year=2014 |isbn=978-0-691-15822-8 |edition=Revised color}}</ref>{{rp|52}} Two distinct [[point (geometry)|points]] in a [[Plane (geometry)|plane]] are always [[Necessity and sufficiency|sufficient]] to define a unique [[line (geometry)|line]] in a nontrivial [[Euclidean space]].<ref>{{Cite book |last=Carrell |first=Jim |url=https://personal.math.ubc.ca/~carrell/307_chap1.pdf |title=MATH 307 Applied Linear Algebra |chapter=Chapter 1 {{!}} Euclidean Spaces and Their Geometry}}</ref>

A [[Set theory|set]] that is a [[field (mathematics)|field]] has a minimum of two [[Element (mathematics)|elements]].<ref>{{cite web| url=https://proofwiki.org/wiki/Field_Contains_at_least_2_Elements|title=Field Contains at least 2 Elements}}</ref>

[[Binary number|Binary]] is a number system with a [[radix|base]] of two, it is used extensively in [[Computer|computing]].<ref>{{Cite web |title=How computers see the world - Binary - KS3 Computer Science Revision |url=https://www.bbc.co.uk/bitesize/guides/z26rcdm/revision/1 |access-date=2024-06-05 |website=BBC Bitesize |language=en-GB}}</ref>

== As a word ==
''Two'' is most commonly a [[English determiners|determiner]] used with [[Grammatical number|plural]] countable nouns, as in ''two days'' or ''I'll take these two''.<ref>{{Cite book |last1=Huddleston |first1=Rodney D. |url=https://www.worldcat.org/oclc/1255524478 |title=A student's introduction to English grammar |last2=Pullum |first2=Geoffrey K. |last3=Reynolds |first3=Brett |publisher=[[Cambridge University Press]] |year=2022 |isbn=978-1-316-51464-1 |edition=2nd |location=Cambridge, United Kingdom |pages=117 |oclc= 1255524478|author-link=Rodney Huddleston |author-link2=Geoffrey K. Pullum}}</ref> ''Two'' is a [[English nouns|noun]] when it refers to the number two as in ''two plus two is four.''

The word ''two'' is derived from the [[Old English]] words {{lang|ang|twā}} ([[Grammatical gender|feminine]]), {{lang|ang|tū}} (neuter), and {{lang|ang|twēġen}} (masculine, which survives today in the form [[wikt:twain|twain]]).<ref name=OED>{{Cite OED|two, adj., n., and adv.}}</ref>

== Evolution of the Arabic digit ==
[[Image:Evolution2glyph.png|x50px|left]]
The digit used in the modern Western world to represent the number 2 traces its roots back to the Indic [[Brahmic script]], where "2" was written as two horizontal lines. The modern [[Chinese written language|Chinese]] and [[Japanese writing system|Japanese]] languages (and Korean [[Hanja]]) still use this method. The [[Gupta script]] rotated the two lines 45&nbsp;degrees, making them diagonal. The top line was sometimes also shortened and had its bottom end curve towards the center of the bottom line. In the [[Devanagari|Nagari]] script, the top line was written more like a curve connecting to the bottom line. In the Arabic [[Ghubār numerals|Ghubar]] writing, the bottom line was completely vertical, and the digit looked like a dotless closing question mark. Restoring the bottom line to its original horizontal position, but keeping the top line as a curve that connects to the bottom line leads to our modern digit.<ref>Georges Ifrah, ''The Universal History of Numbers: From Prehistory to the Invention of the Computer'' transl. David Bellos et al. London: The Harvill Press (1998): 393, Fig. 24.62</ref>

== In science ==
* The first [[Magic number (physics)|magic number]] - number of electrons in the innermost electron shell of an atom.<ref>{{Cite web|url=https://www.sjsu.edu/faculty/watkins/magicnumbers2.htm|title=The Complete Explanation of the Nuclear Magic Numbers Which Indicate the Filling of Nucleonic Shells and the Revelation of Special Numbers Indicating the Filling of Subshells Within Those Shells|website=www.sjsu.edu|access-date=2019-12-22|archive-date=2019-12-02|archive-url=https://web.archive.org/web/20191202130317/http://www.sjsu.edu/faculty/watkins/magicnumbers2.htm|url-status=dead}}</ref>

== See also ==
*[[Binary number]]

== References ==
{{Reflist}}

==External links==
{{Portal|Mathematics}}
{{Commons and category|2 (number)|2 (number)}}
*[http://primes.utm.edu/curios/page.php/2.html Prime curiosities: 2]

{{Wiktionary|two|both}}

{{Integers|zero}}

{{Authority control}}
{{DEFAULTSORT:2 (Number)}}
[[Category:2 (number)]]
[[Category:Integers]]