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This article discusses the number three. For the year AD 3, see 3. For other uses of 3, see 3 (disambiguation)
3 (three) is a number, numeral, and glyph. It is the natural number following 2 and preceding 4.
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In mathematics
Three is the first odd prime number, and the second smallest prime after two. It is both the first Fermat prime (22º + 1) and the first Mersenne prime (22 - 1), as well as the first lucky prime. However, it's the second Sophie Germain prime, the second Mersenne prime exponent, the second factorial prime (2! + 1), the second Lucas prime, the second Stern prime.
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. In the Perrin sequence, however, 3 is both the zeroeth and third Perrin numbers.
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.
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In numeral systems
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Evolution of the glyph
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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
In fonts with text figures, 3 usually has a descender, for example, , though in some French fonts it has an ascender instead of a descender.
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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.
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In science
White light is composed of the mixture of the three additive primary hues: red, green, and blue.
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Astronomy
There are three types of galaxies.
Globular Cluster M3 (also known as Messier Object 3 or NGC 5272) is a globular cluster in the Canes Venatici constellation.
The Roman numeral III (usually) stands for the third-discovered satellite of a planet or minor planet (e.g. Pluto III)
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Chemistry
There are three basic states: liquid, solid, and gas
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Physics
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Abrahamic religions
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.
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 leaders of the Jewish nation during their 40 years of wandering in the desert: Moses, Aaron, and Miriam
There are three divisions of Jews: Kohen, Levi, and Israel
Hamantaschen, a filled cookie served on Purim, has 3 corners which represent the biblical Haman's ears or his pockets.
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Other religions
The three Gunas underlie action, in the Vedic system of knowledge. There is also the concept of Trimurti in Hindu tradition.The Buddha has three bodies.The three Vedas are called trayi i.e triad. Lord Shiva is Trinetra-Three-eyed. The confluence of the Ganga, Yamuna and hidden Sarasvati is the famous Triveni-confluence of three rivers.Buddhism's three refuges are Trisharana- Buddhan sharanam gacchami, Dhammam sharanam gacchami, Sangham sharanam gacchami.
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In esoteric tradition
Feri Tradition teaches of the existence of three souls in each individual person.
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In philosophy
Plato split his utopian city into three populations: laborers, guardians (warriors), and philosophers (rulers)
Further, Plato split the soul into three parts: the appetitive, the spirted, and the rational
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As a lucky or unlucky number
Three (三, formal writing: 叁, pinyin san1, Cantonese: saam1) is considered a good number in Chinese culture because it sounds like the word "alive" (生 pinyin sheng1, Cantonese: saang1), compared to four (四, pinyin: si4, Cantonese: sei3) that sounds like the word "death" (死 pinyin si3, Cantonese: sei2).
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.
Luck, especially bad luck, is often said to "come in threes".
Some cultures in history have a place for people of third gender.
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In technology
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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.
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.
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In music
Three is the number of performers in a trio.
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.
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.
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In filmography
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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. The number 3 position in the batting order is generally occupied by the team's best hitter. Babe Ruth, widely regarded as the greatest player in baseball history, wore the number 3.
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 die 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 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.
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In other fields
For other uses and related terms, see also 3 (disambiguation)
Three is:
Three is a mobile phone operator.
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 the charm" (or, rarely, "Three time's the charm") usually means that the third time a person attempts something, he or she will succeed
Three-bean salad is an appetizer containing three types of beans, such as kidney, yellow, and green beans
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.
3 is the number of novels or films in a trilogy(such as 'The Lord of the Rings') and the number of interconnected works of art in a triptych
3 is the amount of sister needed to make up the 'charmed ones' from WB's television show 'charmed.' Without 3 witches the charmed ones, or the most powerful witches in time, could not exist.
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Historical years
'''3 A.D.''', 3 B.C., 1903, 2003, etc.
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