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.

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.<ref>Template:Cite book</ref> 2 is the smallest and the only even prime number, and the first Ramanujan prime.<ref>Template:Cite web</ref> It is also the first superior highly composite number,<ref>Template:Cite web</ref> and the first colossally abundant number.<ref>Template:Cite web</ref>

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;<ref>Template:Cite OEIS</ref> 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.<ref name="Wilson2014">Template:Cite book</ref>Template:Rp Two distinct points in a plane are always sufficient to define a unique line in a nontrivial Euclidean space.<ref>Template:Cite book</ref>

A set that is a field has a minimum of two elements.<ref>Template:Cite web</ref>

Binary is a number system with a base of two, it is used extensively in computing.<ref>Template:Cite web</ref>

As a word

Two is most commonly a determiner used with plural countable nouns, as in two days or I'll take these two.<ref>Template:Cite book</ref> 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 Template:Lang (feminine), Template:Lang (neuter), and Template:Lang (masculine, which survives today in the form twain).<ref name=OED>Template:Cite OED</ref>

Evolution of the Arabic digit

File:Evolution2glyph.png

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.<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 - number of electrons in the innermost electron shell of an atom.<ref>Template:Cite web</ref>

See also

• Binary number

External links

• Prime curiosities: 2