2

← 1 2 3 →
−1 0 1 2 3 4 5 6 7 8 9 → List of numbers; Integers; ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	two
Ordinal	2nd (second / twoth)
Numeral system	binary
Factorization	prime
Gaussian integer factorization
Prime	1st
Divisors	1, 2
Greek numeral	Β´
Roman numeral	II, ii
Greek prefix	di-
Latin prefix	duo-/bi-
Old English prefix	twi-
Binary	102
Ternary	23
Senary	26
Octal	28
Duodecimal	212
Hexadecimal	216
Greek numeral	β'
Arabic, Kurdish, Persian, Sindhi, Urdu	٢
Ge'ez	፪
Bengali	২
Chinese numeral	二，弍，貳
Devanāgarī	२
Telugu	౨
Tamil	௨
Kannada	೨
Hebrew	ב
Armenian	Բ
Khmer	២
Maya numerals	••
Thai	๒
Georgian	Ⴁ/ⴁ/ბ(Bani)
Malayalam	൨
Babylonian numeral	𒐖
Egyptian hieroglyph, Aegean numeral, Chinese counting rod	\|\|
Morse code	.._ _ _

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.

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), tū (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] It is also the first superior highly composite number,^[5] and the first colossally abundant number.^[6]

Geometry

A digon is a polygon with two sides (or edges) and two vertices.^[7]^: 52 Two distinct points in a plane are always sufficient to define a unique line in a nontrivial Euclidean space.^[8]

Set theory

A set that is a field has a minimum of two elements.^[9] A Cantor space is a topological space $2^{\mathbb {N} }$ 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.^[10]

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	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
2^x	2	4	8	16	32	64	128	256	512	1024		2048	4096	8192	16384	32768	65536	131072	262144	524288	1048576
x²	1	4	9	16	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.^[11]

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

In science

The number of polynucleotide strands in a DNA double helix.^[12]
The first magic number.^[13]
The atomic number of helium.^[14]

References

^ 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.
^ ^a ^b "two, adj., n., and adv.". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ Sloane, N. J. A. (ed.). "Sequence A005843 (The nonnegative even numbers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2022-12-15.
^ "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.
^ "A002201 - OEIS". oeis.org. Retrieved 2024-11-28.
^ "A004490 - OEIS". oeis.org. Retrieved 2024-11-28.
^ Wilson, Robin (2014). Four Colors Suffice (Revised color ed.). Princeton University Press. ISBN 978-0-691-15822-8.
^ Carrell, Jim. "Chapter 1 | Euclidean Spaces and Their Geometry". MATH 307 Applied Linear Algebra (PDF).
^ "Field Contains at least 2 Elements".
^ "How computers see the world - Binary - KS3 Computer Science Revision". BBC Bitesize. Retrieved 2024-06-05.
^ 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
^ "Double-stranded DNA". Scitable. Nature Education. Archived from the original on 2020-07-24. Retrieved 2019-12-22.
^ "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.
^ Bezdenezhnyi, V. P. (2004). "Nuclear Isotopes and Magic Numbers". Odessa Astronomical Publications. 17: 11. Bibcode:2004OAP....17...11B.

External links

Prime curiosities: 2

[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.

[OED-2] "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] "A002201 - OEIS". oeis.org. Retrieved 2024-11-28.

[6] "A004490 - OEIS". oeis.org. Retrieved 2024-11-28.

[Wilson2014-7] Wilson, Robin (2014). Four Colors Suffice (Revised color ed.). Princeton University Press. ISBN 978-0-691-15822-8.

[8] Carrell, Jim. "Chapter 1 | Euclidean Spaces and Their Geometry". MATH 307 Applied Linear Algebra (PDF).

[9] "Field Contains at least 2 Elements".

[10] "How computers see the world - Binary - KS3 Computer Science Revision". BBC Bitesize. Retrieved 2024-06-05.

[11] 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

[12] "Double-stranded DNA". Scitable. Nature Education. Archived from the original on 2020-07-24. Retrieved 2019-12-22.

[13] "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.

[14] Bezdenezhnyi, V. P. (2004). "Nuclear Isotopes and Magic Numbers". Odessa Astronomical Publications. 17: 11. Bibcode:2004OAP....17...11B.

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