3 (number)

This article discusses the number three. For the year AD 3, see 3. For other uses of 3, see 3 (disambiguation) tre-/ter- (from Latin)


Cardinal	3 three
Ordinal	3rd third
Numeral system	ternary
Factorization	prime
Divisors	1, 3
Roman numeral	III
Unicode representation of Roman numeral	Ⅲ, ⅲ
prefixes	tri- (from Greek)
Binary	11
Octal	3
Duodecimal	3
Hexadecimal	3
Hebrew	ג (Gimel)
Arabic	٣

3 (three) is a number, numeral, and glyph. It is the natural number following 2 and preceding 4.

In mathematics

Three is the first odd prime number, and the second smallest prime after two.
Three is the first Fermat prime (2^2º + 1).
Three is the first Mersenne prime (2² - 1).
Three is the second Sophie Germain prime.
Three is the second Mersenne prime exponent.
Three is the first lucky prime.
Three is the first Genocchi prime.
Three is the second factorial prime (2! + 1).
Three is the first unique prime due to the properties of its reciprocal.
Three is the second triangular number.
Three is the only prime which is one less than a perfect square. Any other number which is one less than a perfect square will be the product of the numbers one more than, and one less than, the square root of said square.
Three non-collinear points determine a plane and a circle.
Three is the fourth Fibonacci number and the third that is unique. It is also the second Lucas prime and the second Stern prime.
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..). See also Divisibility rule.
A triangle is the most durable shape possible, the only "perfect" figure which if all endpoints have hinges will never change its shape unless the sides themselves are bent.
3 is the only integer between e and π.

The Arabic 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): ٣

, though in some French fonts it has an ascender instead of a descender.

Pointed version

A common variant of the digit 3 has a pointed top, similar to the character ezh, sometimes used to prevent people from falsifying a 3 into an 8.

In science

Three is the atomic number of lithium.
White light is composed of the mixture of the three primary hues: red, green, and blue.

Astronomy

Globular Cluster M3 (also known as Messier Object 3 or NGC 5272) is a globular cluster in the Canes Venatici constellation.

In religion

The Holy Trinity in Christian doctrine (or trinity in general), is God both as a single entity and as three entities: the Father, the Son and the Spirit. This is also known as Tripartite division.
The Three Wise Men visited Jesus after his birth
A devout Muslim tries to make a pilgrimage to all three holy cities in Islam: Mecca, Medina, and Jerusalem
King Solomon states in Ecclesiastes 4:12: "A three-ply cord is not easily severed." Examples of this concept of three-ness in Judaism are:

The three Patriarchs: Abraham, Isaac, and Jacob
The three pilgrim festivals (Sheloshet HaRegalim): Passover, Shavuot, and Sukkot
The three leaders of the Jewish nation during their 40 years of wandering in the desert: Moses, Aaron, and Miriam
The Tanakh is comprised of 3 sections: Torah, Nevi'im, and Ketuvim
There are 3 daily prayer services: Shacharit, Mincha, and Maariv
There are three divisions of Jews: Kohen, Levi, and Israel
Shimon Hatzaddik taught: "On three things the world stands: On Torah, on prayer, and on acts of kindness" (Pirkei Avoth 1:2). Rabban Shimon ben Gamliel taught: "The world continues to exist because of three things: justice, truth, and peace" (ibid. 1:18)

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

As a lucky or unlucky number

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 that sounds like the word "death".

Counting to three is common in situations where a group of people wish to perform an action in synchrony: Now, on the count of three, everybody pull! Assuming the counter is proceeding at a uniform rate, the first two counts are necessary to establish the rate, but then everyone can predict when "three" will come based on "one" and "two"; this is likely why three is used instead of some other number.

Some computer users may use "3" as an alternate to the letter "E", often in jest or to prevent search engines from reading their messages. This form of code is an example of basic Leetspeak.

Luck, especially bad luck, is often said to "come in threes".

Most cultures in history have a place for people of third gender.

In technology

On computer keyboards, the "3" key may be used to type the pound sign.
On most telephone keypads, the "3" key is also associated with the letters "D", "E", and "F".
In ASCII, the code for "3" in hexadecimal is 33. This is the only character in ASCII such that a large file consisting of a single character has identical-looking hexadecimal and normal representation.
The glyph "3" may be used as a subsitute for yogh () when that character is not available.
Three is the minimum odd number of voting components for simple easy redundancy checks by direct comparison.
Three is approximately pi (actually closer to 3.14159) when doing rapid engineering wags or estimates. The same is true if one wants a rough-and-ready estimate of e, which is actually approximately 2.7183.

In music

In music, the Roman numeral iii is the mediant scale degree, chord, or diatonic function, when distinguished III = major and iii = minor.

The 3|4 time signature of Western classical music tradition (Three beats to a measure, with the quarter note comprising the beat.) is said to represent the Holy Trinity of Christian doctrine, Father, Son and Holy Spirit. It is for this reason that it is often utilized in compositions which were written for use in ecclesiastical rites, or that are inspired by scriptural/spiritual themes and texts.

Three is important to popular American rock group, The White Stripes, and has become one of the trademarks of their style. Their third single was entitled The Big Three Killed My Baby and in 2005 their lead singer has changed his name to Three Quid.

It is also is in the name of many music groups, including Three Dog Night, 3 Doors Down, Three Days Grace, and 3 Inches of Blood. The band (3) uses the number alone as its moniker.

Béla Bartók wrote three piano concertos. Camille Saint-Saëns wrote three completed, numbered symphonies.

The third song on the album Protection by Massive Attack is called Three. The lyrics refer continually to the perceived magical properties of the number.

In sports

In rugby union, 3 is the jersey number of the starting tighthead prop. It is also the number of points received for a successful drop goal or penalty kick.
In baseball, 3 is the number of strikes before the batter is out and the number of outs per side per inning. It also represents the first baseman's position.
In basketball, a shot made from behind the three-point arc.
Also in basketball, 3 represents the small forward position.
Retired number of former baseball players Babe Ruth, Joe Medwick, Bill Terry, Harmon Killebrew, and Dale Murphy.
Is the number of the famous NASCAR stock car that Dale Earnhardt drove for nearly 20 years before his death in 2001. He won 6 out of his 7 championships while driving the #3 car. No one has driven the 3 car since his death.
In American football, 3rd down is the do or decide down. If insufficient yardage is gained to achieve a first down, which starts a new series of downs, then coach/quarterback/coach in charge (CIC)/team is faced with fourth down: Shall we attempt immediate success and risk failure and giving other side good field position ... or punt to establish good defensive position while other side is on offensive?
In both American and Canadian football, the number of points received for a successful field goal.
In Canadian football, the last down before a team loses possession on downs. Usually, a team faced with a third down will punt (if far from the opponent's goal line) or attempt a field goal (if relatively close).
An Ironman triathlon consists of three events, a 2.4 mile (3.86 kilometer) swim, a 112 mile (180.2 kilometer) bike ride, and a 26.2 mile (42.2 kilometer) marathon run.

In other fields

For other uses and related terms, see also 3 (disambiguation)

Three is:

Three is a mobile phone operator.
The number of stars in "Pacific's triple star" in the God Defend New Zealand, one of New Zealand's two national anthems.
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 phrase "Third time's a charm" usually means the third time a person attempts something, they will succeed.
The television VHF channel most often used for hooking up VCRs and/or video game systems. If it is otherwise occupied by a local broadcaster, then channel 4 is used instead.
On most phones, the 3 key is associated with the letters D, E, and F, but on the BlackBerry it is the key for U and I.
The designation of the Crowsnest Highway in Alberta and British Columbia.
"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, The Dale Earnhardt Story.
No. 3 - 1997 Korean gangster comedy written and directed by Neung-han Song
- "the magic number", according to De La Soul.
- "the magic number", according to Multiplication Rock.
Among children, or when otherwise calling for subtlety, the phrase "number 3" can refer to the act of vomiting, masturbation or to experiencing diarrhea. Since the phrases "number 1" and "number 2" are more common, "number 3" is used less, and its meanings are more vague.
In Astrology, Gemini is the 3rd astrological sign of the Zodiac.
The number 3 is often used as a literary device to provoke a feeling of unnaturalness, as twos are much more common in nature (limbs, hemispheres, eyes, etc). This is a prevailing theme in Ray Bradbury's novel Fahrenheit 451. The aliens and their machines in the 2005 film War of the Worlds were associated with features recurring in threes: eyes, legs, fingers, etc, for this same reason.
Three Rings of Power were wielded by the Elves in J. R. R. Tolkien's Middle-earth legendarium.
In tarot, card No. 3 is "the Empress"

Historical years

3 A.D., 3 B.C., 1903, 2003, etc.

External links

Tricyclopedic Book of Threes

Famous numbers | Integers

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