Four

Two forms of four.

The four (4) is the natural number that follows three and precedes five.

The 4 in mathematics

Arithmetic and algebraic properties

• The 4 is the first composite number, its divisors being 1, the 2 and himself. As the sum of its own dividers is 3 ≤ 4, it is a defective and sublime number. The next composite number is 6.
• The 4 is the third natural number that is square perfect if you admit natural zero. The previous one is the 1 and the next is the 9.
• 4 is the square of 2.
• If you multiply a number by 4 you get the quadruple the initial number, and divides a number by 4 you get a Room the initial number.
• The difference of two perfect squares of the same parity(i.. both pairs or both odds) is multiple of four.
• If a number is formed exactly by two different prime factors, the number of dividers is four.
• A number written in the binary system (base 2) can be passed to the base numbering system 4, adding each pair of digits, from right to left, the double of the first plus the second. Sea 11011011₍₂₂₎. Add pairs 1, 1; 1.0; 0.1; 1.1; result: 2.1 +1; 2.1 +0; 2.0+1; 2.1+1, or 3123₍₄₎
• The same procedure is done to pass a number, written in the quaternary system, to the hexadecimal numbering system. They separate in pairs from right to left, then the quadruple from the first plus the second. For example, 3212₍₄₎. The first pair 12 da 1×4+2 = 6, the second pair 32 da 3×4+2 = 14 = e. Then it turns e6_(Hx). Both in the decimal system are 230.
• Apparently conmutivity: 24=42=16.{displaystyle 2^{4}=4^{2}=16. !
• There are only two types of algebraic groups four elements: the group H = {0, 1, 2 3} division remains between 4, with the addition; and the group of Klein V = {1, p, q, pq}, in which each element is inverse of itself.
• A tetrairical number.
• A pie number.
• It is a term of the succession of Padovan.

Geometry properties

• A 4-sided polygon is a quadrilateral. If it does not have two parallel sides it is called trapezoid; if it has two parallel sides it is called trapezecio; if it has the parallel sides two to two it is a romboid and if the angles that are formed between the sides are 90° it is called rectangle; if it has the four sides of the same measure, call rombo. Finally, the regular polygon of 4 sides receives the square name, which is both rombo and rectangle.
• A 4-sided polyhedron is a tetrahedron. The faces of the regular tetraedro are equilateral triangles. Within a regular tetrahedron you can register another.
• The square has Four axes of symmetry: the two diagonals and the two dry straights that pass through the midpoints of each pair of opposite sides.
• One of the catetos of a triangle of whole sides measures Four units and forms the pythagorean terna (3.4;5).

Astronomy

• The orbits of the 4 planets of the solar system within the asteroid belt.
• There are 4 earth planets (or rocks) in our solar system: Mercury, Venus, Earth, Mars.
• There are 4 giant gaseous planets of the Solar System: Jupiter, Saturn, Uranus, Neptune.
• The Roman number IV (usually) represents the fourth satellite-discovered of a minor planet or planet (e.g. Jupiter IV).
• Certain ways of writing the 4 correspond to the astronomical sign of Jupiter:
• Messier M4 object is a globular cluster found in the constellation of Scorpio.

Biology

• The number of nitrogenated base types in DNA and RNA is 4: adenine, guanine, cytosine, thymine (uracyl in RNA).
• The heart of the mammals consists of 4 chambers.
• The fourth finger of a human hand (which on the left hand is the ring finger) moves when the tiny finger moves.
• There are 4 human blood groups (A, B, O and AB).
• Humans have 4 wheels of judgment.

Technology

• The identification code used in recycling to identify low-density polyethylene.
• Most furniture (tables, chairs, closets) has 4 legs.
• The 4 process colors (CMYK) are used for printing.
• The wide use of the rectangle (with 4 angles and 4 sides), since they have the form of cash and adjacence capacity close to each other (houses, rooms, tables, bricks, paper sheets, screens, movie frames).
• Credit cards have from 4 to 12 function keys.
• In most phones, the 4 key is associated with the G, H and I letters, but on the BlackBerry phone is the key to the D and F.
• On many computer keyboards, the "4" key can also be used with the dollar ($) sign if the key is pressed.
• It's the bit number in a nibbleWhich is half a byte.
• On the Internet argot, 4 can replace the word ‘for’ (as in English) four (4) and for (‘para’) are pronounced similarly. For example, you can write "4u" (four you) instead of ‘for you’ (for you).

Other sciences

• A tetrahmer is formed by 4 sub-units.
• It's the atomic number of the beryllium.

The 4 in religions

• Traditionally there are also 4 elements: land, water, air and fire.
• In Christian symbolology 4 has a certain importance:

• The Genesis (2:10-14) describes that 4 rivers are born in the Garden of Eden towards the 4 cardinal points. These 4 rivers are: the Pisón (El Jaxartes Sri Daria), the Guijón (El Amu Daria), the Hiddekel (the Tigris), and the P’rat (the Euphrates).
• There are 4 Gospels canonical Christians, attributed to the four evangelists (Matthew, Mark, Luke and John).
• In the Revelation (4:6-7) of John Evangelist is said to be 4 living creatures full of eyes ahead and behind:

1 like a lion.

2 Like a bull.

3 Like a man.

4 Like an eagle.

• In the same book we talk about the Four Horsemen of Revelation: war, hunger, plague, death.

• In Buddhist religion there are Four noble truths.
• In Chinese culture, it is considered to be 4 (income, Yes.) as a number of bad luck due to its phonetic similarity with the word it means death (s afternoon). This superstition (tetraphobia) is also given in the Japanese culture where the Chinese vocables are maintained, with pronunciation shiLike, you know, you know, like, "Clean words." In Japan, for example, it is considered a bad omen to receive a gift composed of 4 parts or pieces.
• In the Japanese calendar, based on Buddhist religion, the 4th of every month is considered Butsumetsu (the day Buddha died). This is why it is a day of bad omens in which any celebration or journey is avoided. We must add that it is a lunisolar calendar of "six days" (rokuyō) so every six days the Butsumetsu repeat again.

Music

• Four, a musical instrument of the guitar family.
  • Four Puerto Rican, five-string instrument.
  • Four Venezuelans
• Four (2002).
• 4 (2011), Beyoncé album.

The 4 on TV

• Four, Spanish generalist channel, belonging to Mediaset Spain
• TVCuatro, public television from the state of Guanajuato, Mexico.

The 4 in transportation

• Most vehicles, including motor vehicles, and in particular cars/cars and light commercial vehicles with 4 road wheels.
• Quattro, which means four of the Italian language, is used by Audi as a brand to indicate that the four-wheel drive (4WD) technologies are used in Audi-marca cars. The word Quattro was initially used by Audi in 1980 in its original 4WD coupe, the Audi Quattro. Audi also has a privately owned subsidiary company called quattro GmbH.
• The designation of Interstate 4, a highway in Florida, the lowest unqualified number assigned and signed on the United States Interstate Road System.

In other fields

• In NATO's phonetic alphabet, digit 4 is called fower.
• In astrology, Cancer is the fourth astrological sign of the Zodiac.
• Arthur Conan Doyle wrote a book entitled The sign of the four.
• In the game Tetris, each form is made of 4 blocks. Also the game bears the name of tetra, which in Greek for 4.
• In the English language, four is the only number with the same number of letters as their value.
• The 4 belongs to the series of numbers (4, 8, 15, 16, 23 and 42) that appear in the American series Lost (Lost).
• The 4 represents the number of judges in the U.S. Supreme Court required to grant a self-appeal (i.e., according to the case, is one less than the number required to make a decision by a majority).
• Number Four/John Smith of the saga I Am Number Four of Pittacus Lore.
• The four voyages of Christopher Columbus during the discovery of the American continent.

Groups of four

• Four rules: sum, subtraction, multiplication, division.
• The classic elements (fire, air, water, land).
• Every four years there's a biscuit.
• The four seasons: spring, summer, autumn, winter.
• Four parts of a day: morning, noon, evening and night.
• Four cardinal points: north, south, east, west.
• Four temperaments: blood, colric, melancholic and phlematic.
• Method of four corners
• Four card games: hearts, diamonds, clovers, stings.
• Four nations from the United Kingdom: England, Wales, Scotland, Northern Ireland.
• Four haciendas: politics, administration, judiciary, journalism. Especially in the expression "fourth power", which means journalism.
• Four Esquinas is the only place in the United States, where four states unite in one point: Colorado, Utah, New Mexico and Arizona.
• The Fantastic Four: Mr. Fantastic, Invisible Woman, Human Torch and Cosa.
• The Beatles rock band were known as the Fab Four (Fabulous Four): John Lennon, Ringo Starr, George Harrison and Paul McCartney.
• Band of the Four is a British post-punk rock band formed in the 1970s.
• In a classic string quartet there are four performers, usually two violins, one viola and one cello.
• Four food groups (harnic products, dairy products, grain products, and fresh fruits and vegetables). This model is obsolete.
• In the United States and other countries, the full term of office for president lasts four years.
• Many important sporting events (the World Cup of Football, the Olympic Games, etc.), are held every 4 years.
• Number Four/John Smith of the saga I Am Number Four of Pittacus Lore
• The four horsemen of the apocalypse.

Use in Spanish

Four can be both a noun (“the four of cups”) and an adjective (“four books”).

As a multiplicative numeral adjective, the quadruple form is the most common for both genders: «quadruple prize». Quadruple and quadrupla are rare.

As a partitive or fractional numeral, the adjective cuarta is used (like many other partitives, it coincides with the feminine ordinal form) which is always accompanied by "parte": « three quarters of the votes".

The prefixes cuadri-, cuatri-, cuadru- of Latin origin, mean 'four': "quadrilateral", "four-motor", "quadruped". Also the prefix tetra- of Greek origin: "tetrahedron".