3 ( three; ) is a number, Numeral system, and glyph. It is the natural number following 2 and preceding 4.
Evolution of the glyph
Three is the largest number still written with as many lines as the number represents. (The
Ancient Rome usually wrote 4 as IIII, but this was almost entirely replaced by the subtractive notation IV in the Middle Ages.) 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 Empire 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 as
३. It was the Western Ghubar
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[Georges Ifrah, The Universal History of Numbers: From Prehistory to the Invention of the Computer transl. David Bellos et al. London: The Harvill Press (1998): 393, Fig. 24.63]
While the shape of the 3 character has an ascender in most modern , in typefaces with text figures the character usually has a descender, as, for example, in . In some French language textfigure typefaces, though, it has an ascender instead of a descender.
Flat top 3
A common variant of the digit 3 has a flat top, similar to the character Ʒ (
ezh). This form is sometimes used to prevent people from fraudulently changing a 3 into an 8. It is usually found on UPCA barcodes and standard 52card decks.
Mathematics
3 is:

a rough approximation of (3.1415...) and a very rough approximation of e (2.71828..) when doing quick estimates.

the number of noncollinear points needed to determine a plane and a circle.

the first odd prime number and the second smallest prime.

the first Fermat prime ().

the first Mersenne prime ().

the second Sophie Germain prime.

the second Mersenne prime exponent.

the second factorial prime ().

the second Lucas prime.

the second triangular number. It is the only prime triangular number.

the fourth Fibonacci number.

the smallest number of sides that a simple (nonselfintersecting) polygon can have.

the only number for which n, n+10 and n+20 are prime.
Three is the only prime which is one less than a square number. Any other number which is for some integer n is not prime, since it is . This is true for 3 as well (with ), but in this case the smaller factor is 1. If n is greater than 2, both and are greater than 1 so their product is not prime.
A natural number is divisible by three if the digital root 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. This works in base 10 and in any positional numeral system whose radix divided by three leaves a remainder of one (bases 4, 7, 10, etc.).
Three of the five Platonic solids have triangular faces – the tetrahedron, the octahedron, and the icosahedron. Also, three of the five Platonic solids have vertices where three faces meet – the tetrahedron, the hexahedron (cube), and the dodecahedron. Furthermore, only three different types of polygons comprise the faces of the five Platonic solids – the triangle, the square, and the pentagon.
There are only three distinct 4×4 .
According to Pythagoras and the Pythagoreanism school, the number 3, which they called triad, is the noblest of all digits, as it is the only number to equal the sum of all the terms below it, and the only number whose sum with those below equals the product of them and itself.
The trisection of the angle was one of the three famous problems of antiquity.
Gauss proved that every integer is the sum of at most 3 triangular numbers.
Numeral systems
There is some evidence to suggest that early man may have used counting systems which consisted of "One, Two, Three" and thereafter "Many" to describe counting limits. Early peoples had a word to describe the quantities of one, two, and three but any quantity beyond was simply denoted as "Many". This is most likely based on the prevalence of this phenomenon among people in such disparate regions as the deep Amazon and Borneo jungles, where western civilization's explorers have historical records of their first encounters with these indigenous people.
List of basic calculations


3 × x  3  6  9  12  15  18  21  24  27  30  33  36  39  42  45  48  51  54  57  60  63  66  69  72  75  150  300  3000  30000 


3 ÷ x  3  1.5  1  0.75  0.6  0.5  0.  0.375  0.  0.3
!  0.  0.25  0.  0.2  0.2  0.1875  0.1  0.1  0.1  0.15 
x ÷ 3  0.  0.  1  1.  1.  2  2.  2.  3  3.
!  3.  4  4.  4.  5  5.  5.  6  6.  6. 


3  3  9  27  81  243  729  2187  6561  19683  59049
!  177147  531441  1594323  4782969  14348907  43046721  129140163  387420489  1162261467  3486784401 
x  1  8  27  64  125  216  343  512  729  1000
!  1331  1728  2197  2744  3375  4096  4913  5832  6859  8000 
Science

The Roman numeral III stands for giant star in the Yerkes spectral classification scheme.

Three is the atomic number of lithium.

Three is the ASCII code of "End of Text".

Three is the number of dimensions that humans can perceive. Humans perceive the universe to have three spatial dimensions, but some theories, such as string theory, suggest there are more.

The triangle, a polygon with three edges and three vertices, is the most stable physical shape. For this reason it is widely utilized in construction, engineering and design.
[" Most stable shape triange". Maths in the city. Retrieved February 23, 2015.]

The ability of the human eye to distinguish is based upon the varying sensitivity of different cells in the retina to light of different wavelengths. Humans being Trichromacy, the retina contains three types of color receptor cells, or cone cell.
protoscience">
Protoscience

In European alchemy, the three primes (Latin: tria prima) were salt (), sulfur () and mercury ().
[Eric John Holmyard. Alchemy. 1995. p.153][Walter J. Friedlander. The golden wand of medicine: a history of the caduceus symbol in medicine. 1992. p.7677]

The three doshas (weaknesses) and their are the basis of Ayurvedic medicine in India.
Pseudoscience

Three is the symbolic representation for Mu, Augustus Le Plongeon's and James Churchward's lost continent.
Philosophy

Philosophers such as Aquinas, Immanuel Kant, Hegel, C. S. Peirce, and Karl Popper have made threefold divisions, or trichotomies, which have been important in their work.

Hegel's dialectic of Thesis + Antithesis = Synthesis creates threeness from twoness.
Religion
Many world religions contain triple deities or concepts of trinity, including:
Christianity

The threefold office of Christ is a Christian doctrine that Christ performs the functions of prophet, priest, and king.

The ministry of Jesus lasted approximately three years (27–30 AD).

During the Agony in the Garden, Christ asked three times for the chalice to be taken from his lips.

Jesus rose from the dead on the third day after his death (Sunday, April 9, 30 AD).

The devil tempted Jesus three times.

Saint Peter thrice denied Jesus and thrice affirmed his faith in Jesus

The Biblical magi – wise men who were astronomers/astrologers from Persia – gave Jesus three gifts.

There are three Synoptic Gospels and three epistles of John.

Paul the Apostle went blind for three days after his conversion to Christianity.
Judaism

Noah had three sons: Ham, Shem and Japheth

The Three Patriarchs: Abraham, Isaac and Jacob

The prophet Balaam beat his donkey three times.

The prophet Jonah spent three days and nights in the belly of a large fish

Three divisions of the Written Torah: Torah (Five Book of Moses), Nevi'im (Prophets), Ketuvim (Writings)

Three divisions of the Jewish people: Kohen, Levite, Yisrael

Three daily Jewish prayer: Shacharit, Mincha, Maariv

Three Shabbat meals

Shabbat ends when three stars are visible in the night sky

Three Pilgrimage Festivals: Passover, Shavuot, Sukkot

Three on the Passover Seder table

The Three Weeks, a period of mourning bridging the fast days of Seventeenth of Tammuz and Tisha B'Av

Three cardinal sins for which a Jew must die rather than transgress: idolatry, murder, sexual immorality

Upsherin, a Jewish boy's first haircut at age 3

A Beth din is composed of three members

Potential converts are traditionally turned away three times to test their sincerity

In the Jewish mysticism tradition of the Kabbalah, it is believed that the soul consists of three parts, with the highest being neshamah ("breath"), the middle being ruach ("wind" or "spirit") and the lowest being Nephesh ("repose").
[Kaplan, Aryeh. " The Soul". Aish. From The Handbook of Jewish Thought (Vol. 2, Maznaim Publishing. Reprinted with permission.) September 4, 2004. Retrieved February 24, 2015.] Sometimes the two elements of Chayah ("life" or "animal") and Yechidah ("unit") are additionally mentioned.

In the Kabbalah, the Tree of Life (Hebrew: Etz haChayim, עץ החיים) refers to a latter 3pillar diagrammatic representation of its central mystical symbol, known as the Sephirot.
Buddhism

The Triple Bodhi (ways to understand the end of birth) are Budhu, Pasebudhu, and Mahaarahath.

The Three Jewels, the three things that Buddhists take refuge in.
Shinto

The Imperial Regalia of Japan of the sword, mirror, and jewel.
Daoism
Hinduism
Zoroastrianism

The three virtues of Humata, Hukhta and Huvarshta (Good Thoughts, Good Words and Good Deeds) are a basic tenet in Zoroastrianism.
Norse mythology
Three is a very significant number in
Norse mythology, along with its powers 9 and 27.

Prior to Ragnarök, there will be three hard winters without an intervening summer, the Fimbulwinter.

Odin endured three hardships upon the World Tree in his quest for the runic alphabet: he hanged himself, wounded himself with a spear, and suffered from hunger and thirst.

Borr had three sons, Odin, Vili, and Vé.
Other religions

The Rule of Three.

The Triple Goddess: Maiden, Mother, Crone; the three fates.

The sons of Cronus: Zeus, Poseidon, and Hades.

The Slavic god Triglav has three heads.
Esoteric tradition

The Theosophical Society has three conditions of membership.

Gurdjieff's Three Centres and the Fourth Way.

Liber AL vel Legis, the central scripture of the religion of Thelema, consists of three chapters, corresponding to three divine narrators respectively: Nuit, Hadit and RaHoorKhuit.

The Triple Greatness of Hermes Trismegistus is an important theme in Hermeticism.
As a lucky or unlucky number
Three (三, formal writing: 叁,
pinyin sān,
Cantonese:
saam^{1}) is considered a
numerology in
Chinese culture because it sounds like the word "alive" (生 pinyin
shēng, Cantonese:
saang^{1}), compared to four (四, pinyin:
sì, Cantonese:
sei^{1}), which sounds like the word "death" (死 pinyin
sǐ, Cantonese:
sei^{2}).
Counting to three is common in situations where a group of people wish to perform an action in Synchronization: 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, and the count of "three" is predicted based on the timing of the "one" and "two" before it. Three is likely used instead of some other number because it requires the minimal amount counts while setting a rate.
In East Asia and Southeast Asia, there is a widespread superstition that considers it inauspicious to take a photo with three people in it; it is professed that the person in the middle will die first.
There is another superstition that it is unlucky to take a third light, that is, to be the third person to light a cigarette from the same match or lighter. This superstition is sometimes asserted to have originated among soldiers in the trenches of the First World War when a sniper might see the first light, take aim on the second and fire on the third.
The phrase "Third time's the charm" refers to the superstition that after two failures in any endeavor, a third attempt is more likely to succeed. This is also sometimes seen in reverse, as in "third man to gets caught".
Luck, especially bad luck, is often said to "come in threes".[See " bad" in the Oxford Dictionary of Phrase and Fable, 2006, via Encyclopedia.com.]
Sports

In American and Canadian football, a field goal is worth 3 points.

In association football:

For purposes of league standings, almost all leagues award three points for a win.

A team that wins three trophies in a season is said to have won a treble.

In baseball:

A batter Strikeout upon the third Strike zone in any single batting appearance.

Each team's half of an inning ends once the defense has recorded 3 outs (unless the home team has a walkoff hit in the ninth inning or any extra inning).

In scorekeeping, "3" denotes the first baseman.

In basketball:

3 points are awarded for a basket made from behind a designated arc on the floor.

The "3 position" is the small forward.

In bowling, three strikes bowled consecutively is known as a "turkey".

In cricket, a bowler who is credited with dismissals of batsmen on three consecutive deliveries has achieved a "hattrick".

In Gaelic games (Gaelic football for Gaelic football and women, hurling, and camogie), 3 points are awarded for a goal, scored when the ball passes underneath the crossbar and between the goal posts.

In ice hockey:

Scoring three goals is called a "hat trick" (usually not hyphenated in North America).

A team will typically have three forwards on the ice at any given time.

In professional wrestling, a pin is when one holds the opponent's shoulders against the mat for a count of three.

In rugby union:

A successful penalty kick for goal or drop goal is worth 3 points.

In the French variation of the bonus points system, a team receives a bonus point in the league standings if it wins a match while scoring at least 3 more tries than its opponent.

A "threepeat" is a term for winning three consecutive championships.

A triathlon consists of three events: swimming, bicycling, and running.

In many sports a competitor or team is said to win a Triple Crown if they win three particularly prestigious competitions.
See also

Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group. (1987): 46–48
External links