The four (4) is a natural number between three and five. She is straight and a square number.
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Four straight. It is the first composite number, and thus the first non- prime number after one.
The peculiarity of the four is that both and therefore applies. This can even be generalized using the arrow notation. It applies to any natural:
A four-sided face is a quadrilateral. A geometric shape with four faces is a tetrahedron.
The four-color theorem states that four colors suffice to color so all areas on a map that nowhere abut the same color space, whereas three colors for it are not enough.
Another feature of the four is the impossibility of an algebraic equation of higher degree than four with the help of root extraction, and simple arithmetic basic operations dissolve. The mathematician Niels Henrik Abel published in 1826 his proof at the moment.
The number has, depending on age and language different glyphs:
The Roman letters IV, the fourth Arab In Urdu (India, Pakistan) is 4, Devanagari (India ), it is 4 and in Hebrew ד. There are in today's Latin script two options for typography: The Four connecting line to the left above with the arms of the cross and without.
The Latin word for four is quattuor, the corresponding ordinal quartus ( fourth ) and the adjective quadrus (square) found in the German input in terms such as quarter, fourth, quartile, quartet or square.
The Greek prefix for four τετρα - (tetra - ) was used as tetralogy, Tetrarchy, tetrahedron or tetrachord in foreign words.
The energy stored in the deoxyribonucleic acid of the genome information of all earthly life is coded in triplet sequences, which consist of four basic units: the nucleobases adenine ( A), thymine (T ), guanine (G) and cytosine (C).
The tetrapods, the four-footed land vertebrates, are in principle four extremities, whose basic meaning is locomotion. Individual tetrapods, all or some limbs back or reshuffled have such as snakes, which have no lokomotionsfähigen more extremities or the person in which the forelimbs are no longer suitable for locomotion. Among the tetrapods include amphibians ( amphibian ), reptiles ( reptiles), mammals and birds.
The number 4 is the atomic number of the alkaline earth metal beryllium in the periodic table.
In orthopedics, the four characters is a clinical test for testing the function of the hip joint in humans. Here, lying one leg is bent transversely to the axis of the body to a four.
Culture, literature, music, society and intellectual life
The Greek natural philosophers saw four elements (fire, water, earth, air) as basic components of all being: the four - element theory works up to the present time. Since there are four elements in addition to the four cardinal directions, seasons and temperaments, which was four in the Middle Ages as the number of earthly things, as opposed to three, the number of God and the Trinity. Seven and Twelve: From the mathematical connections of these numbers three and four is more holy in Christianity figures emerge. From this Christian doctrine of numbers obtained for the music of the opinion that the 3/4-time is regarded as the perfect - shown earlier by a circle, while the 4/4-time is considered the imperfect, the underground, the in until today the musical notation is indicated by a semi- circle, the large C -like characters.
In the symbolism of numbers it is, inter alia the cross. Both in its presentation it intersects, and the cross has four corners. It is therefore in general for the death and suffering. In Chinese numerology and also in Korea and Japan, the Four is considered an unlucky number, because they sound (Chinese四, pinyin sì ) is similar to the Chinese word for death (死Chinese, Pinyin sǐ ) see: Tetra phobia.
The back number 4 is considered as the number of pre- Oppers / central defender in football.