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{{Short description|Number}}

{{about|the number|the year|AD 1|other uses|One (disambiguation)|and|Number One (disambiguation)}}
{{Contains special characters}}
{{Infobox number
|number=1
|numeral=[[Unary numeral system|unary]]
|factorization=[[Empty product|∅]]
|divisor=1
|roman =I, i
|greek prefix=[[Wiktionary:mono-|mono-]]/[[Wiktionary:haplo-|haplo-]]
|latin prefix=[[Wiktionary:uni-|uni-]]
|lang1=[[Greek numeral]]
|lang1 symbol=α'
|lang2=[[Eastern Arabic numerals|Arabic]], [[Central Kurdish|Kurdish]], [[Persian language|Persian]], [[Sindhi language|Sindhi]], [[Urdu numerals|Urdu]]
|lang2 symbol={{resize|150%|١}}
|lang3=[[Assamese language|Assamese]] & [[Bengali language|Bengali]]
|lang3 symbol={{resize|150%|১}}
|lang4=[[Chinese numeral]]
|lang4 symbol=一/弌/壹
|lang5=[[Devanāgarī]]
|lang5 symbol={{resize|150%|१}}
|lang6=[[Ge'ez alphabet|Ge'ez]]
|lang6 symbol={{resize|150%|፩}}
|lang7=[[Georgian numerals|Georgian]]
|lang7 symbol={{resize|130%|Ⴀ/ⴀ/ა}}([[Ani (letter)|Ani]])

|lang8=[[Hebrew numerals|Hebrew]]
|lang8 symbol=[[aleph|{{resize|150%|א}}]]
|lang9=[[Japanese numeral]]
|lang9 symbol=一/壱
|lang10=[[Kannada language|Kannada]]
|lang10 symbol={{resize|150%|[[೧]]}}
|lang11=[[Khmer numerals|Khmer]]
|lang11 symbol={{resize|150%|១}}
|lang13=[[Malayalam]]
|lang13 symbol=൧
|lang14=[[Meitei language|Meitei]]
|lang14 symbol={{resize|150%|꯱}}
|lang15=[[Thai numerals|Thai]]
|lang15 symbol={{resize|150%|๑}}
|lang16=[[Tamil language|Tamil]]
|lang16 symbol={{resize|150%|௧}}
|lang17=[[Telugu language|Telugu]]
|lang17 symbol={{resize|150%|೧}}
|lang18=[[counting rods|Counting rod]]
|lang18 symbol=𝍠}}

'''1''' ('''one''', '''unit''', '''unity''') is a [[number]] representing a single or the only [[entity]]. 1 is also a [[numerical digit]] and represents a single [[unit (measurement)|unit]] of [[counting]] or [[measurement]]. For example, a [[line segment]] of ''unit length'' is a line segment of [[length]] 1. In conventions of sign where zero is considered neither positive nor negative, 1 is the first and smallest [[Positive number|positive integer]].<ref name=":0">{{Cite web|last=Weisstein|first=Eric W.|title=1|url=https://mathworld.wolfram.com/1.html|access-date=2020-08-10|website=mathworld.wolfram.com|language=en|archive-date=2020-07-26|archive-url=https://web.archive.org/web/20200726111421/https://mathworld.wolfram.com/1.html|url-status=live}}</ref> It is also sometimes considered the first of the [[sequence (mathematics)|infinite sequence]] of [[natural number]]s, followed by [[2]], although by other definitions 1 is the second natural number, following [[0]].

The fundamental mathematical property of 1 is to be a [[multiplicative identity]], meaning that any number multiplied by 1 equals the same number. Most if not all properties of 1 can be deduced from this. In advanced mathematics, a multiplicative identity is often denoted 1, even if it is not a number. 1 is by convention not considered a [[prime number]]; this was not universally accepted until the mid-20th century. Additionally, 1 is the smallest possible difference between two distinct [[natural number]]s.

The unique mathematical properties of the number have led to its unique uses in other fields, ranging from science to sports. It commonly denotes the first, leading, or top thing in a group.

== As a word ==
''One'' is most commonly a [[English determiners|determiner]] used with [[Grammatical number|singular]] countable nouns, as in ''one day at a time''.<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> ''One'' is also a [[English pronouns|pronoun]] used to refer to an unspecified person or to people in general as in ''one should take care of oneself''.<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=140 |oclc=1255524478}}</ref> Finally, ''one'' is a [[English nouns|noun]] when it refers to the number one as in ''one plus one is two'' and when it is used as a [[Pro-form|pro form]], as in ''the green one is nice'' or ''those ones look good.''

=== Etymology ===
''One'' comes from the English word ''an'',<ref name="etymonline">{{cite web |title=Online Etymology Dictionary |url=http://www.etymonline.com/index.php?term=one |website=etymonline.com |publisher=Douglas Harper |access-date=2013-12-30 |archive-date=2013-12-30 |archive-url=https://web.archive.org/web/20131230234708/http://www.etymonline.com/index.php?term=one |url-status=live }}</ref> which comes from the Proto-Germanic root {{not a typo|''*ainaz''}}.<ref name="etymonline" /> The Proto-Germanic root {{not a typo|''*ainaz''}} comes from the Proto-Indo-European root ''*oi-no-''.<ref name="etymonline" />

Compare the Proto-Germanic root {{not a typo|''*ainaz''}} to [[Old Frisian]] ''an'', [[Gothic language|Gothic]] ''ains'', [[Danish language|Danish]] ''en'', [[Dutch language|Dutch]] ''een'', [[German language|German]] ''eins'' and [[Old Norse]] ''einn''.

Compare the Proto-Indo-European root ''*oi-no-'' (which means "one, single"<ref name="etymonline" />) to [[Greek language|Greek]] ''oinos'' (which means "ace" on dice<ref name="etymonline" />), [[Latin]] ''unus'' (one<ref name="etymonline" />), [[Old Persian]] {{not a typo|''aivam''}}, [[Old Church Slavonic]] ''-inu'' and ''ino-'', [[Lithuanian language|Lithuanian]] ''vienas'', [[Old Irish]] ''oin'' and [[Breton language|Breton]] ''un'' (one<ref name="etymonline" />).

== As a number ==
One, sometimes referred to as '''unity''',<ref name=":0" /><ref>Skoog, Douglas. ''Principles of Instrumental Analysis''. Brooks/Cole, 2007, p. 758.</ref> is the first non-zero [[natural number]]. It is thus the [[integer]] after [[zero]].

Any number multiplied by one remains that number, as one is the [[Identity element|identity]] for [[multiplication]]. As a result, 1 is its own [[factorial]], its own [[Square (algebra)|square]] and [[square root]], its own [[Cube (algebra)|cube]] and [[cube root]], and so on. One is also the result of the [[empty product]], as any number multiplied by one is itself. It is also the only natural number that is neither [[composite number|composite]] nor [[prime number|prime]] with respect to [[Division (mathematics)|division]], but is instead considered a [[unit (ring theory)|unit]] (meaning of [[ring theory]]).

== As a digit ==
[[File:Clock 24 J.jpg|thumb|alt=Decorative clay/stone circular off-white sundial with bright gold stylized sunburst in center of the 24-hour clock face, one through twelve clockwise on right, and one through twelve again clockwise on left, with J shapes where ones' digits would be expected when numbering the clock hours. Shadow suggests 3 PM toward the lower left.|The 24-hour tower clock in [[Venice]], using ''J'' as a symbol for 1]][[File:Woodstock typewriter, 1940s, daylight - keyboard.jpg|thumb|This Woodstock typewriter from the 1940s lacks a separate key for the numeral 1.]][[File:Mediaevalziffern.svg|thumb|[[Hoefler Text]], a typeface designed in 1991, represents the numeral 1 as similar to a small-caps I.]]
{{main|History of the Hindu–Arabic numeral system}}
The glyph used today in the Western world to represent the number 1, a vertical line, often with a [[serif]] at the top and sometimes a short horizontal line at the bottom, traces its roots back to the [[Brahmi numerals|Brahmic]] script of ancient India, where it was a simple vertical line. It was transmitted to Europe via [[Arabic numerals|the Maghreb and Andalusia]] during the Middle Ages, through scholarly works written in [[Arabic]].

In some countries, the serif at the top is sometimes extended into a long upstroke, sometimes as long as the vertical line, which can lead to confusion with the glyph used for [[7|seven]] in other countries. In styles in which the digit 1 is written with a long upstroke, the digit 7 is often written with a horizontal stroke through the vertical line, to disambiguate them. Styles that do not use the long upstroke on digit 1 usually do not use the horizontal stroke through the vertical of the digit 7 either.

While the shape of the character for the digit 1 has an [[Ascender (typography)|ascender]] in most modern [[typeface]]s, in typefaces with [[text figures]], the glyph usually is of [[x-height]], as, for example, in [[File:TextFigs148.svg|alt=Horizontal guidelines with a one fitting within lines, a four extending below guideline, and an eight poking above guideline]].

Many older typewriters lack a separate key for ''1'', using the lowercase letter ''l'' or uppercase ''I'' instead. It is possible to find cases when the uppercase ''J'' is used, though it may be for decorative purposes. In some typefaces, different glyphs are used for I and 1, but the numeral 1 resembles a [[small caps]] version of I, with parallel serifs at top and bottom, with the capital I being full-height.

== Mathematics ==
===Definitions===
Mathematically, 1 is:
*in [[arithmetic]] ([[algebra]]) and [[calculus]], the [[natural number]] that follows [[0 (number)|0]] and the multiplicative [[identity element]] of the [[integer]]s, [[real number]]s and [[complex number]]s;
*more generally, in [[algebra]], the '''multiplicative identity''' (also called ''unity''), usually of a [[group (mathematics)|group]] or a [[ring (mathematics)|ring]].

Formalizations of the natural numbers have their own representations of 1. In the [[Peano axioms]], 1 is the [[Successor function|successor]] of 0. In ''[[Principia Mathematica]]'', it is defined as the set of all [[singleton (mathematics)|singletons]] (sets with one element), and in the [[Von Neumann cardinal assignment]] of natural numbers, it is defined as the [[Set (mathematics)|set]] {0}.

In a multiplicative [[group (mathematics)|group]] or [[monoid]], the [[identity element]] is sometimes denoted 1, but ''e'' (from the German ''Einheit'', "unity") is also traditional. However, 1 is especially common for the multiplicative identity of a ring, i.e., when an addition and 0 are also present. When such a ring has [[Characteristic (algebra)|characteristic]] ''n'' not equal to 0, the element called 1 has the property that {{nowrap|''n''1 {{=}} 1''n'' {{=}} 0}} (where this 0 is the additive identity of the ring). Important examples are [[finite field]]s.

By definition, 1 is the [[magnitude (mathematics)|magnitude]], [[absolute value]], or [[Norm (mathematics)|norm]] of a [[unit complex number]], [[unit vector]], and a [[identity matrix|unit matrix]] (more usually called an identity matrix). The term ''unit matrix'' is sometimes used to mean something [[Matrix of ones|quite different]].

By definition, 1 is the [[probability]] of an event that is absolutely or [[almost certain]] to occur.

In [[category theory]], 1 is sometimes used to denote the [[terminal object]] of a [[category (mathematics)|category]].

In [[number theory]], 1 is the value of [[Legendre's constant]], which was introduced in 1808 by [[Adrien-Marie Legendre]] in expressing the [[Asymptotic analysis|asymptotic behavior]] of the [[prime-counting function]]. Legendre's constant was originally conjectured to be approximately 1.08366, but was proven to equal exactly 1 in 1899.

===Properties===
[[Tally mark|Tallying]] is often referred to as "base 1", since only one mark – the tally itself – is needed. This is more formally referred to as a [[unary numeral system]]. Unlike [[base 2]] or [[base 10]], this is not a [[positional notation]].

Since the base 1 exponential function (1<sup>''x''</sup>) always equals 1, its [[inverse function|inverse]] does not exist (which would be called the [[logarithm]] base 1 if it did exist).

In many mathematical and engineering problems, numeric values are typically ''normalized'' to fall within the [[unit interval]] from 0 to 1, where 1 usually represents the maximum possible value in the range of parameters. Likewise, [[vector space|vectors]] are often normalized into [[unit vector]]s (i.e., vectors of magnitude one), because these often have more desirable properties. Functions, too, are often normalized by the condition that they have [[integral]] one, maximum value one, or [[square integrable|square integral]] one, depending on the application.

Because of the multiplicative identity, if ''f''(''x'') is a [[multiplicative function]], then ''f''(1) must be equal to 1.

There are two ways to write the real number 1 as a [[recurring decimal]]: as 1.000..., and as [[0.999...]]. 1 is the first [[figurate number]] of every kind, such as [[triangular number]], [[pentagonal number]] and [[centered hexagonal number]], to name just a few.

1 is also the first and second number in the [[Fibonacci number|Fibonacci]] sequence (0 being the zeroth) and is the first number in many other [[Sequence|mathematical sequences]].

The definition of a [[field (mathematics)|field]] requires that 1 must not be equal to [[zero|0]]. Thus, there are no fields of characteristic 1. Nevertheless, abstract algebra can consider the [[field with one element]], which is not a singleton and is not a set at all.

1 is the most common leading digit in many sets of data, a consequence of [[Benford's law]].

1 is the only known [[Tamagawa number]] for a simply connected algebraic group over a number field.

The [[generating function]] that has all coefficients equal to 1 is a [[geometric series]], given by

<math> \frac{1}{1-x} = 1+x+x^2+x^3+ \ldots </math>

The zeroth [[metallic mean]] is 1, with the [[Golden ratio#Continued fraction and square root|golden section]] equal to the [[Continued fraction#Motivation and notation|continued fraction]] [1;1,1,...], and the infinitely [[Nested radical#Infinitely nested radicals|nested square root]] <math>\scriptstyle\sqrt{1+\sqrt{\text{ }1+\cdots\text{ }}}.</math>

The series of [[unit fraction]]s that most rapidly converge to 1 are the [[multiplicative inverse|reciprocals]] of [[Sylvester's sequence]], which generate the infinite [[Egyptian fraction]]

<math>1 = \frac12 + \frac13 + \frac17 + \frac1{43} + \cdots</math>

===Primality===
{{Main|Prime number#Primality of one}}
1 is by convention neither a [[prime number]] nor a [[composite number]], but a [[unit (ring theory)|unit]] (meaning of [[ring theory]]) like −1 and, in the [[Gaussian integers]], ''[[imaginary unit|i]]'' and −''i''.

The [[fundamental theorem of arithmetic]] guarantees [[factorization|unique factorization]] over the integers only up to units. For example, {{nowrap|4 {{=}} 2{{sup|2}}}}, but if units are included, is also equal to, say, {{nowrap|(−1){{sup|6}} × 1{{sup|23}} × 2{{sup|2}},}} among infinitely many similar "factorizations".

1 appears to meet the naïve definition of a prime number, being evenly divisible only by 1 and itself (also 1). As such, some mathematicians considered it a prime number as late as the middle of the 20th century, but mathematical consensus has generally and since then universally been to exclude it for a variety of reasons (such as complicating the fundamental theorem of arithmetic and other theorems related to prime numbers).

1 is the only positive integer divisible by exactly one positive integer, whereas prime numbers are divisible by exactly two positive integers, composite numbers are divisible by more than two positive integers, and [[0|zero]] is divisible by all positive integers.

=== Table of basic calculations ===
{|class="wikitable" style="text-align: center; background: white"
|-
! style="width:105px;"|[[Multiplication]]
!1
!2
!3
!4
!5
!6
!7
!8
!9
!10
! style="width:5px;"|
!11

!12
!13
!14
!15
!16
!17
!18
!19
!20
! style="width:5px;"|
!21
!22
!23
!24
!25
! style="width:5px;"|
!50
!100
!1000
|-
|'''1 × ''x'''''
|'''1'''
|[[2 (number)|2]]
|[[3 (number)|3]]
|[[4 (number)|4]]
|[[5 (number)|5]]
|[[6 (number)|6]]
|[[7 (number)|7]]
|[[8 (number)|8]]
|[[9 (number)|9]]
|[[10 (number)|10]]
!
|[[11 (number)|11]]
|[[12 (number)|12]]
|[[13 (number)|13]]
|[[14 (number)|14]]
|[[15 (number)|15]]
|[[16 (number)|16]]
|[[17 (number)|17]]
|[[18 (number)|18]]
|[[19 (number)|19]]
|[[20 (number)|20]]
!
|[[21 (number)|21]]
|[[22 (number)|22]]
|[[23 (number)|23]]
|[[24 (number)|24]]
|[[25 (number)|25]]
!
|[[50 (number)|50]]
|[[100 (number)|100]]
|[[1000 (number)|1000]]
|}

{|class="wikitable" style="text-align: center; background: white"
|-
! style="width:105px;"|[[Division (mathematics)|Division]]
!1
!2
!3
!4
!5
!6
!7
!8
!9
!10
! style="width:5px;"|
!11
!12
!13
!14
!15
|-
|'''1 ÷ ''x'''''
|'''1'''
|0.5
|0.{{overline|3}}
|0.25
|0.2
|0.1{{overline|6}}
|0.{{overline|142857}}
|0.125
|0.{{overline|1}}
|0.1
!
|0.{{overline|09}}
|0.08{{overline|3}}
|0.{{overline|076923}}
|0.0{{overline|714285}}
|0.0{{overline|6}}
|-
|'''''x'' ÷ 1'''
|'''1'''
|2
|3
|4
|5
|6
|7
|8
|9
|10
!
|11
|12
|13
|14
|15
|}

{|class="wikitable" style="text-align: center; background: white"
|-
! style="width:105px;"|[[Exponentiation]]
!1
!2
!3
!4
!5
!6
!7
!8
!9
!10
! style="width:5px;"|
!11
!12
!13
!14
!15
!16
!17
!18
!19
!20
|-
|'''1{{sup|''x''}}'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
!
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|'''1'''
|-
|'''''x''{{sup|1}}'''
|'''1'''
|2
|3
|4
|5
|6
|7
|8
|9
|10
!
|11
|12
|13
|14
|15
|16
|17
|18
|19
|20
|}

== In technology ==
[[File:U+2673 DejaVu Sans.svg|50px|right|alt=Chasing-arrow triangle with numeral one within|1 as a resin identification code, used in recycling]]
* The [[resin identification code]] used in recycling to identify [[polyethylene terephthalate]].<ref>{{cite web |url=http://www.americanchemistry.com/s_plastics/bin.asp?CID=1102&DID=4645&DOC=FILE.PDF |title=Plastic Packaging Resins |publisher=American Chemistry Council |url-status=dead |archive-url=https://web.archive.org/web/20110721103005/http://www.americanchemistry.com/s_plastics/bin.asp?CID=1102&DID=4645&DOC=FILE.PDF |archive-date=2011-07-21 }}</ref>
*The [[International Telecommunication Union|ITU]] country code for the [[North American Numbering Plan]] area, which includes the United States, Canada, and parts of the Caribbean.
*A [[binary code]] is a sequence of 1 and [[0 (number)|0]] that is used in [[computer]]s for representing any kind of [[data]].
*In many physical devices, 1 represents the value for "on", which means that electricity is flowing.<ref name=Woodford>{{citation |first=Chris |last=Woodford |author1-link=Chris Woodford (author) |url=https://books.google.com/books?id=My7Zr0aP2L8C&pg=PA9 |title=Digital Technology |date=2006 |publisher=Evans Brothers |isbn=978-0-237-52725-9 |page=9 |access-date=2016-03-24 |archive-date=2023-01-22 |archive-url=https://web.archive.org/web/20230122151342/https://books.google.com/books?id=My7Zr0aP2L8C&pg=PA9 |url-status=live }}</ref><ref name=Godbole>{{citation |first=Achyut S. |last=Godbole |url=https://books.google.com/books?id=SN_46YHs27MC&pg=PA34 |title=Data Comms & Networks |date=1 September 2002 |publisher=Tata McGraw-Hill Education |isbn=978-1-259-08223-8 |page=34}}</ref>
*The numerical value of [[Boolean data type|true]] in many programming languages.
*1 is the [[ASCII]] code of "[[Start-of-Header|Start of Header]]".

== In science ==
*[[Dimensionless quantities]] are also known as quantities of dimension one.
*1 is the atomic number of [[hydrogen]].
*+1 is the [[electric charge]] of [[positron]]s and protons.
*Group 1 of the [[periodic table]] consists of the [[alkali metals]].
*Period 1 of the periodic table consists of just two elements, [[hydrogen]] and [[helium]].
*The dwarf planet [[Ceres (dwarf planet)|Ceres]] has the minor-planet designation 1 Ceres because it was the first asteroid to be discovered.
*The Roman numeral I often stands for the first-discovered satellite of a [[planet]] or [[minor planet]] (such as Neptune I, a.k.a. [[Triton (moon)|Triton]]). For some earlier discoveries, the Roman numerals originally reflected the increasing distance from the primary instead.

== In philosophy ==
In the philosophy of [[Plotinus]] (and that of other [[neoplatonist]]s), [[Plotinus#The One|The One]] is the ultimate reality and source of all existence.<ref>{{Cite book|title=The Essentials of Christian Thought: Seeing Reality through the Biblical Story|last=Olson|first=Roger|year=2017|isbn=9780310521563|location=Zondervan Academic}}</ref> [[Philo#Numbers|Philo of Alexandria]] (20 BC – AD 50) regarded the number one as God's number, and the basis for all numbers ("De Allegoriis Legum," ii.12 [i.66]).

The Neopythagorean philosopher [[Nicomachus|Nicomachus of Gerasa]] affirmed that one is not a number, but the source of number. He also believed the [[2 (number)|number two]] is the embodiment of the origin of [[Other (philosophy)|otherness]]. His [[number theory]] was recovered by [[Boethius]] in his Latin translation of Nicomachus's treatise ''[[Introduction to Arithmetic]]''.<ref>{{cite journal|url=https://www.cambridge.org/core/journals/british-journal-for-the-history-of-science/article/abs/from-abacus-to-algorism-theory-and-practice-in-medieval-arithmetic/7DFF144C90C127E715CA40083254E601#access-block|title=From Abacus to Algorism: Theory and Practice in Medieval Arithmetic|journal=The British Journal for the History of Science|volume=10|issue=2|date=July 1, 1977|page=Abstract|doi=10.1017/S0007087400015375|publisher=Cambridge University PRess|author=British Society for the History of Science|s2cid=145065082|access-date=May 16, 2021|archive-date=May 16, 2021|archive-url=https://web.archive.org/web/20210516110812/https://www.cambridge.org/core/journals/british-journal-for-the-history-of-science/article/abs/from-abacus-to-algorism-theory-and-practice-in-medieval-arithmetic/7DFF144C90C127E715CA40083254E601#access-block|url-status=live}}</ref>

== In sports ==
In many professional sports, the number 1 is assigned to the player who is first or leading in some respect, or otherwise important; the number is printed on his or her sports uniform or equipment. This is the [[pitcher]] in [[baseball]], the [[Goalkeeper (association football)|goalkeeper]] in [[association football]] (soccer), the starting [[Fullback (rugby league)|fullback]] in most of [[rugby league]], the starting [[Rugby union positions#Prop|loosehead prop]] in [[rugby union]] and the previous year's world champion in [[Formula One]]. 1 may be the lowest possible player number, like in the American–Canadian [[National Hockey League]] (NHL) since the 1990s{{when|date=November 2021}} or in [[American football]].

== In other fields ==
*''Number One'' is [[Royal Navy]] informal usage for the chief executive officer of a ship, the captain's deputy responsible for discipline and all normal operation of a ship and its crew.
*1 is the value of an [[ace]] in many playing card games, such as [[cribbage]].
*[[List of highways numbered 1]]
*[[List of public transport routes numbered 1]]
*1 is often used to denote the [[Gregorian calendar]] month of [[January]].
*[[1 CE]], the first year of the [[Common Era]]
*01, the former dialling code for [[Greater London]] (now 020)
*For Pythagorean [[numerology]] (a [[pseudoscience]]), the number 1 is the number that means beginning, new beginnings, new cycles, it is a unique and absolute number.
*[[PRS One]], a German paraglider design
*+1 is the code for international telephone calls to countries in the [[North American Numbering Plan]].
* In some countries, a [[house numbering|street address]] of "1" is considered prestigious and developers will attempt to obtain such an address for a building, to the point of lobbying for a street or portion of a street to be renamed, even if this makes the address less useful for wayfinding. The construction of a new street to serve the development may also provide the possibility of a "1" address. An example of such an address is the [[Apple Infinite Loop|Apple Campus]], located at 1 Infinite Loop, [[Cupertino, California]].

== See also ==
{{portal|Mathematics}}
*[[−1]]
*[[+1 (disambiguation)]]
*[[List of mathematical constants]]
*[[One (word)]]
*[[Root of unity]]
*[[List of highways numbered 1]]

== References ==

{{reflist}}

== External links ==

*[https://web.archive.org/web/20140201161542/http://numdic.com/1 The Number 1]
*[http://www.positiveintegers.org/1 The Positive Integer 1]
*[http://primes.utm.edu/curios/page.php/1.html Prime curiosities: 1]

{{Integers|zero}}

{{Authority control}}

{{DEFAULTSORT:1 (Number)}}

{{#seo:
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|description=1 is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For ...
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[[Category:1 (number)| ]]
[[Category:Integers]]

1 - Revision history

MetaBOT at 04:27, 15 July 2023