2 (number)

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Pronunciation of the number 2
 2 Cardinal 2 two Ordinal number 2nd second Numeral system binary Factorization prime Gaussian integer factorization $(1 + i)(1 - i)$ Divisors 1, 2 Greek numeral β' Roman numeral II Roman numeral (Unicode) Ⅱ, ⅱ Arabic ٢ Ge'ez ፪ Bengali ২ Chinese numeral 二，弍，贰，貳 Devanāgarī २ Hebrew ב (Bet) Khmer ២ Korean 이 Thai ๒ prefixes di- (from Greek) duo- bi- (from Latin) twi- (Old English) Binary 10 Octal 2 Duodecimal 2 Hexadecimal 2

2 (two; pronounced too) is a number, numeral, and glyph. It is the natural number after one and before three. In Roman numerals, it is II.

In mathematics

Two has many properties in math. For example: $1 + 1 = 2$. [1] A full number is even if it can be divided by 2. If the last digit of a number is even, then the number is also even. This means that 2 times anything ends in 0, 2, 4, 6, or 8.

Two is the smallest, first, and only even prime number. The next prime number is three. Two and three are the only prime numbers next to each other.

It is the third Fibonacci number, and the third and fifth Perrin numbers.

Fractions with 2 in the denominator do not yield infinite decimal expansions, as is the case with most primes, because 2 is a factors of ten, the decimal base.

Two is the base of the binary system used in computers. The binary way is the simplest system of numbers in which natural numbers can be written.

Two also has the unique property that 2+2 = 2·2 = 2².

Powers of two are central to the concept of Mersenne primes, and important to computer science. Two is the first Mersenne prime exponent.

The square root of two was the first known irrational number.

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 1000
$2 \times x$ 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 2000
Division 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
$2 \div x$ 2 1 $0.\overline{6}$ 0.5 0.4 $0.\overline{3}$ $0.\overline{285714}$ 0.25 $0.\overline{2}$ 0.2 $0.\overline{18}$ $0.1\overline{6}$ $0.\overline{153846}$ $0.\overline{142857}$ $0.1\overline{3}$
$x \div 2$ 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5
Exponentiation 1 2 3 4 5 6 7 8 9 10 11 12 13
$2 ^ x\,$ 2 4 8 16 32 64 128 256 512 1024 2048 4096 8192
$x ^ 2\,$ 1 4 9 16 25 36 49 64 81 100 121 144 169

References

1. Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group. (1987): 41–44