# 2

2 (two) is a number, numeral and digit. It is the natural number following 1 and preceding 3. It is the smallest and the only even prime number.

 ← 1 2 3 →
Cardinaltwo
Ordinal2nd (second / twoth)
Numeral systembinary
Factorizationprime
Gaussian integer factorization${\displaystyle (1+i)(1-i)}$
Prime1st
Divisors1, 2
Greek numeralΒ´
Roman numeralII, ii
Greek prefixdi-
Latin prefixduo-/bi-
Old English prefixtwi-
Binary102
Ternary23
Senary26
Octal28
Duodecimal212
Hexadecimal216
Greek numeralβ'
Arabic, Kurdish, Persian, Sindhi, Urdu٢
Ge'ez
Bengali
Chinese numeral二，弍，貳
Devanāgarī
Telugu
Tamil
Kannada
Hebrewב
ArmenianԲ
Khmer
Maya numerals••
Thai
Georgian Ⴁ/ⴁ/ბ(Bani)
Malayalam
Babylonian numeral𒐖
Egyptian hieroglyph, Aegean numeral, Chinese counting rod||
Morse code.._ _ _

Because it forms the basis of a duality, it has religious and spiritual significance in many cultures.

## As a word

Two is most commonly a determiner used with plural countable nouns, as in two days or I'll take these two.[1] Two is a noun when it refers to the number two as in two plus two is four.

### Etymology of two

The word two is derived from the Old English words twā (feminine), (neuter), and twēġen (masculine, which survives today in the form twain).[2]

The pronunciation /tuː/, like that of who is due to the labialization of the vowel by the w, which then disappeared before the related sound. The successive stages of pronunciation for the Old English twā would thus be /twɑː/, /twɔː/, /twoː/, /twuː/, and finally /tuː/.[2]

## Mathematics

An integer is determined to be even if it is divisible by two. When written in base 10, all multiples of 2 will end in 0, 2, 4, 6, or 8.[3] 2 is the smallest and the only even prime number, and the first Ramanujan prime.[4]

### Geometry

A digon is a polygon with two sides (or edges) and two vertices.[5]: 52  Two distinct points in a plane are always sufficient to define a unique line in a nontrivial Euclidean space.[6]

### Set Theory

A set that is a field has a minimum of two elements.[citation needed] A Cantor space is a topological space ${\displaystyle 2^{\mathbb {N} }}$  homeomorphic to the Cantor set.[citation needed]

## Base 2

Binary is a number system with a base of two, it is used extensively in computing.[7]

## List of basic calculations

Multiplication 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 50 100
2 × x 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 100 200
Division 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
2 ÷ x 2 1 0.6 0.5 0.4 0.3 0.285714 0.25 0.2 0.2 0.18 0.16 0.153846 0.142857 0.13 0.125 0.1176470588235294 0.1 0.105263157894736842 0.1
x ÷ 2 0.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
Exponentiation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
2x 2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384 32768 65536 131072 262144 524288 1048576
x2 1 9 25 36 49 64 81 100 121 144 169 196 225 256 289 324 361 400

## Evolution of the Arabic digit

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 and Japanese languages (and Korean Hanja) still use this method. The Gupta script rotated the two lines 45 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 Nagari script, the top line was written more like a curve connecting to the bottom line. In the Arabic 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.[8]

In fonts with text figures, digit 2 usually is of x-height, for example,  .[citation needed]

## References

1. ^ Huddleston, Rodney D.; Pullum, Geoffrey K.; Reynolds, Brett (2022). A student's introduction to English grammar (2nd ed.). Cambridge, United Kingdom: Cambridge University Press. p. 117. ISBN 978-1-316-51464-1. OCLC 1255524478.
2. ^ a b "two, adj., n., and adv.". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
3. ^ Sloane, N. J. A. (ed.). "Sequence A005843 (The nonnegative even numbers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2022-12-15.
4. ^ "Sloane's A104272 : Ramanujan primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Archived from the original on 2011-04-28. Retrieved 2016-06-01.
5. ^ Wilson, Robin (2014). Four Colors Suffice (Revised color ed.). Princeton University Press. ISBN 978-0-691-15822-8.
6. ^ Carrell, Jim. "Chapter 1 | Euclidean Spaces and Their Geometry". MATH 307 Applied Linear Algebra (PDF).
7. ^ "How computers see the world - Binary - KS3 Computer Science Revision". BBC Bitesize. Retrieved 2024-06-05.
8. ^ 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
9. ^ "Double-stranded DNA". Scitable. Nature Education. Archived from the original on 2020-07-24. Retrieved 2019-12-22.
10. ^ "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". www.sjsu.edu. Archived from the original on 2019-12-02. Retrieved 2019-12-22.
11. ^ Bezdenezhnyi, V. P. (2004). "Nuclear Isotopes and Magic Numbers". Odessa Astronomical Publications. 17: 11. Bibcode:2004OAP....17...11B.