*aka ‘two’*
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/ˈtuː/
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(‘2’ is a number, numeral, and glyph)
(it is the natural number following ‘1’ and preceding ‘3’)
(the glyph used in the modern western world to represent the number 2 traces its roots back to the brahmin indians, who wrote “2” as two horizontal lines)
(the modern chinese and japanese languages still use this method)
The Gupta rotated the two lines 45 degrees, making them diagonal, and sometimes also made the top line shorter and made its bottom end curve towards the center of the bottom line.
Apparently for speed, the Nagari started making the top line more like a curve and connecting to the bottom line.
The Ghubar Arabs made the bottom line completely vertical, and now the glyph looks 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 glyph)
(in fonts with text figures, 2 usually is of x-height, for example, .
(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 the 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)
(it is the third Fibonacci number, and the second and fourth Perrin numbers)
Despite being prime, two is also a superior highly composite number, because it is a natural number which has more divisors than any other number scaled relative to the number itself.
The next superior highly composite number is six.
(vulgar fractions with only 2 or 5 in the denominator do not yield infinite decimal expansions, as is the case with all other primes, because 2 and 5 are factors of ten, the decimal base)
(‘two’ is the base of the simplest numeral system in which natural numbers can be written concisely, being the length of the number a logarithm of the value of the number (whereas in base 1 the length of the number is the value of the number itself); the binary system is used in computers)
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for any number x:
x + x = 2 · x
(addition to multiplication)
x · x = x2 multiplication to exponentiation
xx = x↑↑2 exponentiation to tetration
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(in general…)
hyper(x,n,x) = hyper(x,(n + 1),2)
Two also has the unique property that 2 + 2 = 2 · 2 = 22 = 2↑↑2 = 2↑↑↑2, and so on, no matter how high the level of the hyperoperation is.
Two is the only number x such that the sum of the reciprocals of the powers of x equals itself. In symbols
{\displaystyle \sum _{k=0}^{\infty }{\frac {1}{2^{k}}}=1+{\frac {1}{2}}+{\frac {1}{4}}+{\frac {1}{8}}+{\frac {1}{16}}+\cdots =2.}
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This comes from the fact that:
{\displaystyle \sum _{k=0}^{\infty }{\frac {1}{n^{k}}}=1+{\frac {1}{n-1}}\quad {\mbox{for all}}\quad n\in \mathbb {R} >1.}
Powers of two are central to the concept of Mersenne primes, and important to computer science.
Two is the first Mersenne prime exponent.
Taking the square root of a number is such a common mathematical operation, that the spot on the root sign where the exponent would normally be written for cubic roots and other such roots, is left blank for square roots, as it is considered tacit.
The square root of 2 was the first known irrational number.
The smallest field has two elements.
In the set-theoretical construction of the natural numbers, 2 is identified with the set {{∅},∅}.
This latter set is important in category theory: it is a subobject classifier in the category of sets.
Two is a primorial, as well as its own factorial.
Two often occurs in numerical sequences, such as the Fibonacci number sequence, but not quite as often as one does.
Two is also a Motzkin number, a Bell number, an all-Harshad number, a meandric number, a semi-meandric number, and an open meandric number.
Two is the number of n queens problem solutions for n = 4.
With one exception, all known solutions to Znám’s problem start with 2.
Two also has the unique property such that
{\displaystyle \sum _{k=0}^{n-1}2^{k}=2^{n}-1}
and also
{\displaystyle \sum _{k=0}^{n-1}2^{k}=2^{n}-1}
for a not equal to zero
The number of domino tilings of a 2×2 checkerboard is 2.
In n-dimensional space for any n, any two distinct points determine a line.
(for any polyhedron homeomorphic to a sphere, the Euler characteristic is χ = V − E + F = 2, where V is the number of vertices, E is the number of edges, and F is the number of faces
(as of ‘June 2015’, there are only two known Wieferich primes in ‘base 2’)
(with the exception of the sequence 3, 5, 7, the maximum number of consecutive odd numbers that are prime is ‘two’)
(in mathematics and digital electronics, a binary number is a number expressed in the binary numeral system or base-2 numeral system which represents numeric values using two different symbols: typically 0 (zero) and 1 (one))
(the base-2 system is a positional notation with a radix of 2)
(because of its straightforward implementation in digital electronic circuitry using logic gates, the binary system is used internally by almost all modern computers and computer-based devices)
(each digit is referred to as a ‘bit’)
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👈👈👈☜*“THE NUMBERS GAME”* ☞ 👉👉👉
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*🌈✨ *TABLE OF CONTENTS* ✨🌷*
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