3 (three) is the natural number following 2 and preceding 4.
Evolution of the glyph
Three is often the largest number written with as many lines as the number represents. The Romans tired of writing 4 as IIII, but to this day 3 is written as three lines in Roman and Chinese numerals. 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 (2^{2}  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 points form a plane.
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.
Vulgar fractions with 3 in the denominator have a single digit repeating sequences in their decimal expansions, (.000..., .333..., .666..., .999...)
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. Because of this, the reverse of any number that is divisible by three (or indeed, any permutation of its digits) is also divisible by three. For instance, 1368 and its reverse 8631 are both divisible by three (and so are 1386, 3168, 3186, 3618, etc..).
In human culture
Many human cultures have given the concept of threeness 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 threeness from twoness.
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.

3D

Hendiatris  a rhetorical figure employing three words for one thing
 Ternary Logic  a computing system using base three

Threedecker  a ship of three decks
 Threespine stickleback  a type of fish

Threetoed woodpecker
 Threepence  threepenny 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 threecolor technology or perception
 Triclinium  a couch to three sides of table

Tricolor  threecolor 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  threeyear 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  threeletter 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 threestone structure

Trillion  10^{12} (American) 10^{18} (British)
 Trilobate  of three lobes

Trilobite  a marine arthropod

Trilogy  three works on a theme under the same authorship

Trinity  The Christian godhead of Father, Son, and Holy Ghost.

Trio  three musicians or three actors
 Tripartition  division into three parts

Tripod  a threelegged 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
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
 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 stars in "Pacific's triple star" in the NZ National Anthem
 In Astrology, Gemini is the 3rd astrological sign of the Zodiac.
 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 Neunghan Song
 In music,

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
 Threeletter 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.
Last updated: 05072005 04:59:05
Last updated: 05072005 18:09:53