3 (number)

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


Three is the first odd prime number and the second smallest after the two. At the same time it is the first Mersenne prime ( ), the first Fermat prime (), and the second Sophie Germain prime and the second Mersenne prime exponent. It is the fifth number of the Fibonacci sequence and the third, which is unique.

The triangle is the simplest geometric figure in the plane. With the calculation of its sizes dealt trigonometry.

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

Representation by numeral

Three in most writing systems the largest number that is written with the same number of lines as the number represented. So the Romans were transferred to the representation of the four originally IIII to IV, however, three is represented in the Roman numerals, as in Chinese with three strokes - former vertical (III ), the latter horizontally.

The Indian Brahmi number for the three was like the Chinese with three horizontal lines written during the Gupta the three lines more curved represented ( to the figure on the right, 1st and 2nd sketch from the left). The Nagari went on to draw the even horizontal lines at the right end clockwise downward ( see Figure 3). Gradually, they connected the lines with the respective underlying and thus developed a character that looked modern 3 very similar, but with an additional swab at the base ( Fig. 4 & 5). Finally, it was the Arabs of the Maghreb, which eliminated the Ghubar character for the "extra frills " and so ( Fig. 6) modern 3 developed. In contrast, the extra frills for Ostaraber was very important: You made it much larger, while simultaneously rotated the overlying strokes in a horizontal axis. In this way, a three ( 3) that looked like a mirrored Seven developed, with two elevations on the top line.

The Chinese number characters is Chinese三, Pinyin sān, in formal (ie heavy -forgeable ) notation叁Chinese, Pinyin sān. Because the Chinese word similar to the word for " life" ( Chinese生, Pinyin Sheng ) sounds, the three applies in China as a " good number ".


Not all languages ​​have a separate word for the number three. Some languages, such as the Torres Strait Islanders have only words for 1 and 2, which by combining the numbers 3, 4, 5 and 6 are shown. Larger quantities are simply denoted by "a lot". Some Austronesian and Australian languages ​​other hand, have a separate number for the Trinity, the Trial preserved.

In foreign words both from Latin than from Greek is the root tri for three, in tricolor, Triops. Furthermore, the Latin ordinal tertius (the third ) and the Multiplikativform is triplus (triple) terz in the form of roots or triplets received in German foreign words, third and triple mirror.

Three pulses which occur at equal time intervals, make the third pulse predictable. Thus, three strokes are the shortest way to a starting torque or to say like. Therefore, it is sufficient to count to three, when several people to do something at the same moment. Many nursery rhymes count to three.

  • Phrases All good things come in threes.
  • Forever and three days
  • Three crosses beat / make
  • Can not count to three

While in most figures in the formation of atomic number simply an extension is appended to the base number (two - ter, twenty -ster, thirty -ster ), have the numbers 1 and 3 and their compositions irregular shapes ( first, third, one hundred first, one hundred third ).

The atomic number 7 has a shortened and a regular shape with the truncated form, however, more frequently used: seventh and seventh.

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

In Latin, only the numbers from 1-3 (as well Ambō both), the hundreds of ducentī to nōngentī and the plural milia ( thousands ) declined.

Natural sciences

The color perception of the people there are the three primary colors red, yellow and blue, see trichromatic theory. For color perception of the human being has three different color receptor cells ( cones) for different spectral ranges. Likewise, there are the three spatial dimensions width, length and height, or as generalized X, Y and Z. Thus, there is in the calculation of trajectories ( celestial mechanics ) a so-called three-body problem.

A Triceratops was a dreihörniger dinosaurs, Trifolium is the generic name of clover, which has pinnate leaves ternate.

Society and history

Three people are the smallest group, in the case of votes, an absolute majority can be crucial to a decision. Therefore, many small decision-making bodies consist of three members, for instance Chamber of the German judiciary as the trial by jury or the Little Criminal Court.


" Less than three " is a code in the German journalistic parlance. It refers to the informal rule that neither source nor content may be called, the information obtained must be treated strictly confidential and intended solely for the background are (hidden information).

Culture, literature, music, and spiritual life

A consisting of three parts or individual works plant is called in the visual arts as a triptych, in literature and music, mostly as a trilogy. The Western harmony in music is based on the Assign different sounds to triads.

  • Literary works Three, prose by Péter Zilahy, Stuttgart ( Akademie Schloss Solitude ) 2003, ISBN 3-929085-83-6
  • Three, the second volume of Stephen King's The Dark Tower, Munich ( Heyne ) 2005, ISBN 3-453-01215-1

Mythology and religion

The Three shall from time immemorial as a divine or sacred number. The annual and life cycle was seen in many cultures as a trinity. Tags for this are

  • Grow - Fertility - offense
  • Childhood - Adulthood - Age
  • Waxing moon - full moon - waning moon

A trinity of gods ( Triassic) as a symbol of the all-encompassing divinity exists in many cultures.

Polytheistic religions

  • Greek Mythology The trinity of gods Zeus, Poseidon and Hades divided the dominion of men and gods.
  • Many gods and other mythical characters appear in Trinity, the Graces, Furies, Gorgons, Graeae, Hekatonchires, Horen, Cyclops, Fates, Muses and Sirens.


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

Fairy tale

In the tale of the Trinity is as frequent as in mythology. Examples are:

  • Three sons or daughters of the king or of the miller.
  • Three wishes of the ( good ) Fee.
  • Three to existing tests.