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Two

← 1 2 3 →
−1 0 1 2 3 4 5 6 7 8 9
Cardinal two
Ordinal 2nd (second / )
Numeral system binary
Factorization prime
Gaussian integer factorization
Prime 1st
Divisors 1, 2
Roman numeral II
Roman numeral (unicode) Ⅱ, ⅱ
Greek prefix
Latin prefix
Old English prefix
Binary 102
Ternary 23
Quaternary 24
Quinary 25
Senary 26
Octal 28
Duodecimal 212
Hexadecimal 216
Vigesimal 220
Base 36 236
Greek numeral β'
Arabic & Kurdish ٢
Urdu ۲
Ge'ez
Bengali
Chinese numeral 二,弍,贰,貳
Devanāgarī (do)
Telugu
Tamil
Hebrew ב (Bet)
Khmer
Korean 이,둘
Thai

2 (Two; Listeni/ˈt/) is a number, numeral, and glyph. It is the natural number following 1 and preceding 3.

The number two has many properties in mathematics. An integer is called even if it is divisible by 2. For integers written in a numeral system based on an even number, such as decimal and hexadecimal, divisibility by 2 is easily tested by merely looking at the last digit. If it is even, then the whole number is even. In particular, when written in the decimal system, all multiples of 2 will end in 0, 2, 4, 6, or 8. In numeral systems based on an odd number, divisibility by 2 can be tested by having a digital root that is even.

Two is the smallest and first prime number, and the only even prime number (for this reason it is sometimes called "the oddest prime"). The next prime is three. Two and three are the only two consecutive prime numbers. 2 is the first Sophie Germain prime, the first factorial prime, the first Lucas prime, the first Ramanujan prime, and the first Smarandache-Wellin prime. It is an Eisenstein prime with no imaginary part and real part of the form 3n − 1. It is also a Stern prime, a Pell number, the first Fibonacci prime, and a Markov number—appearing in infinitely many solutions to the Markov Diophantine equation involving odd-indexed Pell numbers.


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