3 (number)

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Arabic digits
0	1	2	3	4	5	6	7	8	9

0 1 2 3 4 5 6 7 8 9 >> List of numbers -- Integers 0 10 20 30 40 50 60 70 80 90 >>
Cardinal	3 three
Ordinal	3rd third
Numeral system	ternary
Factorization	prime
Divisors	1, 3
Roman numeral	III
Prefixes	tri-, tria- (Greek) tre- (Latin)
Binary	11
Octal	3
Duodecimal	3
Hexadecimal	3

3 (three) is the natural number following 2 and preceding 4. Prefixes for 3 include tri- (Greek) and tre- Latin.

Contents

1 Evolution of the glyph

Evolution of the glyph

Image:Evolution3glyph.png

Three is often the largest number written with as many lines as the number represents. Even the Romans tired of writing 4 as IIII, and even today in Chinese, 3 is written as three lines. This was the way the Brahmin Indians wrote it, and the Gupta made the three lines more curved. The Nagari started rotating the lines clockwise and ending each line with a slight downward stroke on the right. Eventually they made these strokes connect with the lines below, and evolved it to a character that looks very much like a modern 3 with an extra stroke at the bottom. It was the Western Ghubar Arabs who finally eliminated the extra stroke and created our modern 3. (The "extra" stroke, however, was very important to the Eastern Arabs, and they made it much larger, while rotating the strokes above to lie along a horizontal axis, and to this day Eastern Arabs write a 3 that looks like a mirrored 7 with ridges on its top line).

In mathematics

Three is the second smallest prime number (after two); the next prime number is five. Three is the first Fermat prime (2^2⁰ + 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. For example, the number 21 is divisible by three (3 times 7) and the sum of its digits is 2 + 1 = 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, 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.

3-D
Ternary Logic - a computing system using base three
Three-decker - a ship of three decks
Three-spine stickleback - a type of fish
Three-toed woodpecker
Threepence - three-penny coin
Threesome - trio or else
Thrice - three times
Triad - a group of three
Trialogue - conversation among three
Triangle - polygon with three sides
Triangulation
Triangulum and Triangulum Australe - constellations
Triarchy - government of three
Triassic Period - geologic time
Triathlete - contestant in Triathlon
Triathlon - contest in three sports
Tribrach - metrical foot, in poetry
Triceps - a muscle
Triceratops - a dinosaur
Trichotomy - division into three parts
Trichroism - property of minerals such as tanzanite, andalusite and iolite
Trichromatism - of three-color technology or perception
Triclinium - a couch to three sides of table
Tricolor - three-color flag, as in France, Romania, Moldova
Tricorn - of three corners, e.g., a hat with "tricorned brim"
Tricuspid - of three cusps
Tricycle - (bicycle × 1½)
Tridactyl - of three toes
Trident - of three teeth or prongs
Triennium - three-year time
Trierarch - captain or manager of a trireme
Trifid - cleft into three
Trifocal - a lens (e.g., of eyeglasses) with three focal lengths
Trifoliate - a leaf structure
Triforium - a certain gallery in church
Trifurcate - threeforked or threestemmed
Trigeminus - trigeminal nerve
Triglyph - an architectural ornament distinctive to Doric friezes
Trigon - triangular harp
Trigonometry - a branch of mathematics
Trigram - I Ching thing
Trigraph - three-letter combination
Trihedron - afigure of three meeting planes
Trihybrid - a kind of hybrid
Trilateral - of three sides or parties
Trilingual - able of or expressed in three languages
Triliteral - a word or root of three letters
Trilithon - prehistoric three-stone structure
Trillion - 10¹² (American) 10¹⁸ (British)
Trilobate - of three lobes
Trilobite - a marine arthropod
Trilogy - three works on a theme under the same authorship
Trio - three musicians or three actors
Tripartition - division into three parts
Tripod - a three-legged structure
Triptych - an artwork consisting of three painted or carved panels that are hinged together
Trireme
Triumvirate - government of three
Trivium - grammar+logic+rhetoric ("three roads")
Troika

In chemistry

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

In other fields

The number of (apparent) spatial dimensions in our universe.
The atomic number of lithium
The "third way" is a political term applied to a variety of "third choice" options that some offer as an alternative to dichotomous situations which may otherwise appear polarized.
The number of nitrogenous base types that DNA and RNA have in common.
The number of stars in "Pacific's triple star" in the NZ National Anthem
The TV VHF channel most often used for hooking up VCRs, since it is rarely used by broadcasters. (If it is, then channel 4 is used instead.)
"In Memory of 3" - a phrase about NASCAR driver Dale Earnhardt, who drove the number 3 car. It can also refer to a 2004 ESPN television movie about Earnhardt's life called, 3: The Dale Earnhardt Story.
The designation of the Crowsnest Highway in Alberta and British Columbia.
No. 3 - 1997 Korean gangster comedy written and directed by Neung-han Song
In music,
- the roman numeral iii is the mediant scale degree, chord, or diatonic function, when distinguished III = major and iii = minor.
- "Number Three" is the title of a They Might Be Giants song from the 1986 album They Might Be Giants. It is the third song on the album.
- 3 (band) - a rock band formed by Keith Emerson, Robert Berry and Carl Palmer
- Three (Sugababes Album) is the third album by UK girl group Sugababes, released in 2003.
3 (telecommunications) - a 3G operator in Europe, Australia and Hong Kong
threedegrees - an instant messaging software created by Microsoft
Three Gorges
Three Kingdoms
The Three Stooges
Three-letter abbreviations and acronyms (TLA)
Three links
Three of a kind - a term used in poker, and also a pop/rap group based in the UK (see Three of a kind (rap group))
Three Principles of the People
Three Represents
Three's Company - an American sitcom
Three Years of Natural Disasters
Historical years: 3 A.D., 3 B.C., or 1903
In rugby union, three is the number of the tighthead prop.
In baseball, three represents the first baseman's position.