# Three

Three
3
presentation
Roman III
dual 11
Octal 3
Duodecimal 3
Morse code · · · - -
Arabic ٣
Chinese
Mathematical properties
sign positive
parity odd
Factorization ${\ displaystyle 3}$
Divider 1, 3

The three (3) is the natural number between two and four . It is odd and a prime number .

## mathematics

Three is the first odd prime and the second smallest after two. At the same time it is the first Mersenne prime number ( ), the first Fermat prime number ( ), as well as the second Sophie-Germain prime number and the second Mersenne prime number exponent . It is the fourth number in the Fibonacci sequence and the second that is unique. ${\ displaystyle 2 ^ {2} -1}$${\ displaystyle 2 ^ {2 ^ {0}} + 1}$

The triangle is the simplest geometric figure in the plane. Trigonometry deals with the calculation of its sizes .

Rule of three: If the cross sum of a number is a multiple of three, the underlying number is divisible by three.

## Representation by numerals

The 3 in different representations and fonts
Development to number sign 3

In most writing systems, three is the largest number written with as many strokes as the number represented. The Romans went from the original IIII to IV in the representation of the number 4, but 3 is represented in the Roman numerals , as in Chinese with three lines - the former vertically (III), the latter horizontally .

The Indian Brahmi number for three was written like the Chinese with three horizontal lines, while the Gupta represented the three lines more curved (see the illustration on the right, 1st and 2nd sketch from the left). The Nagari started to draw the horizontal lines at the right end downwards in a clockwise direction (see Fig. 3). Little by little they connected the lines with the one below and thus developed a character that looked very similar to the modern 3, but with an additional smear at the base (see Fig. 4 & 5). After all, it was the Arabs of the Maghreb who removed the "extra curlicue" with the Ghubar script and thus developed the modern 3 (see Fig. 6). In contrast, the extra curlicue was very important to the Eastern Arabs: They made it much larger while at the same time rotating the strokes above in a horizontal axis. This created a three (٣) that looked like a mirrored seven , with two ridges on the top line.

The Chinese numeral is Chinese   , Pinyin sān , in the formal (i.e. difficult to forge) spelling Chinese   , Pinyin sān . Because the Chinese word sounds similar to the term for “alive” ( Chinese   , Pinyin shēng ), three is considered a “good number” in China.

## Linguistic

A triangle in a picture by Angelika Kauffmann

Not all languages have their own numeral for the number three. Some languages ​​like that of the Torres Strait Islanders only know words for the 1 and the 2, which are combined to represent the numbers 3, 4, 5 and 6. Larger quantities are simply referred to as “a lot”. On the other hand, some Austronesian and Australian languages ​​have retained their own number for the trinity, the trial .

In foreign words from both Latin and Greek , the root tri stands for the number three, in tricolor , triops . Further, the Latin atomic number is tertius (the third) and the Multiplikativform triplus (in triplicate) in the form of the roots terz or triple received in German foreign words, third and prismatic .

Count to three

Three impulses that occur at equal time intervals make the third impulse predictable. Thus three beats are the shortest way to announce a starting moment or the like. It is therefore sufficient to count to three if several people are supposed to do something at the same time, e.g. B. in the game scissors, stone, paper . Many counting rhymes also count to three.

Atomic number

While most numbers simply add an ending to the base number to form the ordinal number ( second, twentieth, thirtieth ), the numbers 1 and 3 and their combinations have irregular shapes ( first, third; hundredth, hundredth third ).

The ordinal number for 7 has an abbreviated and a regular form, although the abbreviated form is used more often: seventh and seventh .

In English only the ordinal numbers from 1 to 3 ( first, second, third ) and their compositions ( twenty-first ) have their own forms, the others end in -th ( fourth, fifth, one hundredth ).

Latin

In Latin only the numbers from 1 to 3 (also ambō both), the hundreds from ducentī to nōngentī and the plural mīlia (thousands) are declined.

## science and technology

For color perception , humans have three types of color sensory cells ( cones ) for different spectral ranges. Accordingly, humans see the three basic colors red, yellow and blue, see three-color theory .

In space and geometry, there are three spatial dimensions: width, length and height or, in general, the axis directions X, Y and Z of a coordinate system. The oriented concatenation of 3 directions in space can be illustrated by a three-finger rule, for example in electromagnetism .

Only three points can span (define) an area . The tripod , tripod , tricycle as well as stool and table are definitely on 3 support points without wobbling.

When calculating trajectories ( celestial mechanics ) one comes across the so-called three - body problem .

The three valence quarks in baryons , such as neutrons and protons .

A Triceratops was a three-horned dinosaur, Trifolium is the generic name of the clover, which has three-pinnate leaves. Trilobites were three-lobed arthropods.

The two-sided symmetrical animals develop three cotyledons : endoderm , mesoderm and ectoderm .

## Society and history

Three people are the smallest group in which an absolute majority can tip the balance for a decision. Many small decision-making bodies therefore consist of three members, for example arbors in the German judiciary such as the lay jury or the small criminal chamber . Democratic systems like that of the FRG are mostly based on the three pillars of the legislative, judicial and executive branches.

Teams of 3 people are dynamic and can make decisions quickly, this also applies to social and erotic three-way relationships, compare Dreimäderlhaus , triumvirate . The Scandinavian countries Denmark, Finland and Sweden as well as the Baltic states Estonia, Latvia and Lithuania formed a contact group under the name Drei plus Drei .

## Sports

The triple jump is a discipline of athletics ; Three-way fight and triathlon combine 3 sports disciplines. In volleyball , a team is allowed to touch the ball 3 times, in basketball 3 half steps when dribbling with the ball. Carom billiards is played with 3 mechanically identical balls, possibly as a three-cushion variant.

## journalism

Under three ” is a code in German journalistic usage. It describes the informal rule that neither the source nor the content may be named, the information received must be treated with absolute confidentiality and only intended for the background (hidden information).

## Culture, literature, music and intellectual life

The three monkeys from Nikko

A work consisting of three parts or individual works is called a triptych in the visual arts , and a trilogy in literature and music . The occidental harmony in music is based on the ordering of different tones into triads .

## Mythology and religion

Triskele on the flag of Sicily

Three has been considered a divine or holy number from ancient times. The year and life cycle was seen as a trinity in many cultures. Keywords for it are

• Growth - fertility - passing away
• Childhood - adulthood - old age
• waxing moon - full moon - waning moon

A trinity of gods ( triad ) as a symbol for the all-embracing divinity exists in many cultures.

### Christianity

Three hares picture in a window of Paderborn Cathedral

In the Christian number symbolism, three is the symbol for the Trinity (Trinity) of God from Father, Son and Holy Spirit. Other examples are the Holy Family , the Three Kings, and the resurrection of Christ on the third day.

### fairy tale

The trinity is as common in fairy tales as it is in mythology. Examples are:

• Three sons or daughters of the king or the miller.
• Three wishes from the (good) fairy.
• Three exams to be passed.