The 3 (number) reference article from the English Wikipedia on 24-Jul-2004
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3 (number)

3 (three) is the natural number following 2 and preceding 4.

List of numbers — Integers

<< 0 1 2 3 4 5 6 7 8 9 >>
CardinalThree
OrdinalThird
Numeral systemternary system
Factorizationprime
Roman numeralIII
Binary11
Hexadecimal3

Table of contents
1 In mathematics
2 In human culture
3 Groups of three
4 In other fields

In mathematics

Three is the second smallest prime number (after two); the next prime number is five. Three is the first Fermat prime (220 + 1) as well as the first Mersenne prime (22 - 1). 3 is the second Mersenne prime exponent. 3 is also the first lucky prime.

It is also a factorial prime (2! + 1), and a unique prime due to the properties of its reciprocal.

Three is the second triangular number.

Three is the fourth Fibonacci number and the third that is unique. It is also a Lucas number.

Three is the fourth open meandric number.

Fractions with 3 in the denominator have a single digit repeating sequences in their decimal expansions, (.000..., .333... or .666...)

A natural number is divisible by three if the sum of its digits in base 10 is divisible by 3.

In human culture

Many human cultures have given the concept of three-ness symbolic meanings. The Holy Trinity in Christian doctrine (or trinity in general), is God both a single entity and three entities, the Father, the Son and the Spirit.

The process of synthesis in Hegelianian dialectic creates three-ness from two-ness

The three Doshas (weaknesses) and their antidotes are the basis of Ayurvedic medicine in India. The three Gunas underlie action, in the Vedic system of knowledge. There is also the concept of Trimurti in Hindu tradition.

Three (三, formal writing: 叁, pinyin san1) is considered a good number in Chinese culture because it sounds like the word "alive" (生 pinyin sheng1), compared to four.



Groups of three

A group of three is often called triad.


See also: List of famous trinities, trios, triplets or threesomes


In chemistry

Triacid, Triaminic, Triamcinolone, Triazine, Triazole, Tribromoethanol, Trichloroethylene, Trichlorfon, Trifluralin, Triglyceride, Triglycerophosphate, Triphosphopyridine nucleotide


In other fields