2

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).

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 →
−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)
Numeral system	binary
Factorization	prime
Gaussian integer factorization	${\displaystyle (1+i)(1-i)}$
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
Santali	᱒
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	.._ _ _

Because it forms the basis of a duality, it has religious and spiritual significance in many 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.^[1] 2 is the smallest and the only even prime number, and the first Ramanujan prime.^[2] It is also the first superior highly composite number,^[3] and the first colossally abundant number.^[4]

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;^[5] more generally, in any even base, even numbers will end with an even digit.

A digon is a polygon with two sides (or edges) and two vertices.^[6]: 52 Two distinct points in a plane are always sufficient to define a unique line in a nontrivial Euclidean space.^[7]

A set that is a field has a minimum of two elements.^[8]

Binary is a number system with a base of two, it is used extensively in computing.^[9]

As a word

Two is most commonly a determiner used with plural countable nouns, as in two days or I'll take these two.^[10] Two is a 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 twā (feminine), tū (neuter), and twēġen (masculine, which survives today in the form twain).^[11]

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.^[12]

In science

• The first magic number - number of electrons in the innermost electron shell of an atom.^[13]

See also

• Binary number