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

Template:Numbers digits
CardinalThree
OrdinalThird
Numeral systemternary system
Factorizationprime
Roman numeralIII
Binary11
Hexadecimal3

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). 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 a Fibonacci number (And it is the third different one, too!). It is also a Lucas 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 Hegelian 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 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.

In chemistry

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

In other fields

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