seven

Seven Days of Creation - 1765 book, title page

7 (seven) is the natural number following 6 and preceding 8.

In mathematics

• Seven is the 4th prime number.
• Seven is a Mersenne prime, since 2³ - 1 = 7.
• Seven is the fourth Mersenne prime exponent.
• Seven is the first Newman-Shanks-Williams prime.
• Seven is the third Lucas prime.
• Seven is the first Woodall prime.
• Seven is the second lucky prime.
• Seven is the second safe prime.
• Seven is the fourth factorial prime
• Seven is both a Carol number and a Kynea number.
• Seven is the smallest number that can't be represented as a sum of fewer than four non-zero squares.
• Seven is the fourth self number.
• Seven is the smallest happy number, except for the trivial example of 1.
• Although the divisible by seven (7) test is not well known (especially compared to the popular divisible by three (3) test), there is an easy way to test if a natural number is evenly divisible by seven (7). See also Divisibility rule.

1. Remove the last digit,
2. Double it, and
3. Subtract it from the remaining digits.
4. If the result is negative and there are 2 or more digits, drop the negative sign.
5. Repeat until you end up with a result that is a multiple of seven (7). (i.e. -7, 0, or +7)

For example, the number 1358 is evenly divisible by seven, since:

135 - (8*2) = 119

11 - (9*2) = -7

Using Number Theory the proof is rather simple, once the number n is rewritten in the form:

n = 10a + b

Where:

a is the remaining digits, and

b is the last digit.

Then:

10a + b = 0 (mod 7)

5 * (10a + b) = 0 (mod 7)

49a + a + 5b = 0 (mod 7)

a + 5b - 7b = 0 (mod 7)

a - 2b = 0 (mod 7)

A second divisibility rule was formulated in 2006 in India, by Himanish Ganjoo, a Class 8 student in St. Columba's School Delhi:

1. Remove the last two digits
2. Divide the remaining number by 7
3. Multiply the remainder by 2
4. Add the product to the last two digits
5. If the sum is divisible by 7, the number is also divisible

On March 25, 2007, Ganjoo formulated another variant form of this test, now separating the last 3 digits (in step 1), and multiplying the remainder by 6 (step 3), and then adding the sum to the last 3 digits (originally separated).

For example, 1568 is divisible by 7,

1. 15/7 Remainder = 1
2. Product 1*2 = 2
3. 68 + 2 = 70 (which is divisible by 7)

Hence, 1568 is divisible by 7

• 999,999 divided by 7 is exactly 142,857. Therefore, when a vulgar fraction with 7 in the denominator is converted to a decimal expansion, the result has the same six-digit repeating sequence after the decimal point, but the sequence can start with any of those six digits. For example, 1/7 = 0.142 857 142.... and 2/7 = 0.285 714 285...
• A seven-sided polygon is a heptagon. The regular n-gons for n ≤ 6 can be constructed by compass and straightedge alone, but the regular heptagon cannot. Figurate numbers representing heptagons (including seven) are called heptagonal numbers. Seven is also a centered hexagonal number.
• There are seven frieze groups, the groups consisting of symmetries of the plane whose group of translations is isomorphic to the group of integers.
• A group or a series of seven is a heptad.
• 7 is the only dimension, besides the familiar 3, in which a vector cross product can be defined

In numeral systems

In quaternary, 7 is the smallest prime with a composite sum of digits.

In the English language, 7 is the only 2-syllable natural, positive 1-digit number

List of basic calculations

Division	1	2	3	4	5	6	7	8	9	10
	11	12	13	14	15
Failed to parse (unknown function\div): 7 \div x	7	3.5		1.75	1.4		1	0.875		0.7
				0.5
Failed to parse (unknown function\div): x \div 7							1
				2

Exponentiation	1	2	3	4	5	6	7	8	9	10		11	12	13
	7	49	343	2401	16807	117649	823543	5764801	40353607	282475249		1977326743	13841287201	96889010407
	1	128	2187	16384	78125	279936	823543	2097152	4782969	10000000		19487171	35831808	62748517

Radix	1	5	10	15	20	25	30	40	50	60	70	80	90	100
	110	120	130	140	150	200	250	500	1000	10000	100000	1000000
	1	5

Evolution of the glyph

In the beginning, various Hindus wrote 7 more or less in one stroke as a curve that looks like an uppercase J upside down. The western Ghubar Arabs' main contribution was to make the longer line diagonal rather than straight, though they showed some tendencies to making the character more rectilinear. The eastern Arabs developed the character from a 6-look-alike into an uppercase V-look-alike. Both modern Arab forms influenced the European form, a two-stroke character consisting of a horizontal upper line joined at its right to a line going down to the bottom left corner, a line that is slightly curved in some font variants. As is the case with the European glyph, the Cham and Khmer glyph for 7 also evolved to look like their glyph for 1, though in a different way, so they were also concerned with making their 7 more different. For the Khmer this often involved adding a horizontal line above the glyph.^[1] This is analogous to the horizontal stroke through the middle that is sometimes used in handwriting in the Western world but which is almost never used in computer fonts. This horizontal stroke is, however, important to distinguish the glyph for seven from the glyph for one in writings that use a long upstroke in the glyph for one.

On the seven-segment displays of pocket calculators and digital watches, 7 is the number with the most common glyph variation (0, 6 and 9 also have variant glyphs). Most calculators use three line segments, but on Sharp, Casio, and a few other brands of calculators, 7 is written with four line segments. The reason is that in Japan & Korea 7 is written as ① in the illustration to the right.

While the shape of the 7 character has an ascender in most modern typefaces, in typefaces with text figures the character usually has a descender, as, for example, in .

In science

• The number of spots on a common ladybug.
• With very few exceptions, all mammals' necks have seven bones.
• ROY G. BIV = red, orange, yellow, green, blue, indigo, and violet are the 7 colours of the rainbow.

Chemistry

• The atomic number of nitrogen.
• The number of periods, or horizontal rows of elements, on the periodic table.
• The number of carbon atoms in heptane, a hydrocarbon.
• Halogens are found in group 7 of the periodic table.

Astronomy

• The number of stellar objects in the solar system visible to the naked eye — the Sun, the Moon and the five classical naked eye planets: Mars, Mercury, Jupiter, Venus, and Saturn.
• Messier object M7, a magnitude 3.5 open cluster in the constellation Scorpius.
• The New General Catalogue object NGC 7, a 14th magnitude spiral galaxy in the constellation Sculptor.
• The number of daughters of Atlas in the Pleiades (also called the "seven sisters").
• The number of saints appearing in a constellation called "Saptharishi Mandalam" in Indian astronomy.
• The number of stars in the constellation of Ursa major.
• The Saros number of the solar eclipse series which began on -2590 April 8 and ended on -1310 May 16. The duration of Saros series 7 was 1,280.1 years, and it contained 72 solar eclipses.
• The Saros number of the lunar eclipse series which began on -2595 July 15 and ended on -1008 February 22. The duration of Saros series 7 was 1,586.6 years, and it contained 89 lunar eclipses.
• The Roman numeral VII stands for white dwarfs in the Yerkes spectral classification scheme.
• The Roman numeral VII (usually) stands for the seventh-discovered satellite of a planet or minor planet (e.g., Jupiter VII).

In technology

• The code for international direct dial phone calls to Russia and Kazakhstan.
• The number of digits in an American or Canadian telephone number, excluding the area code.
• The seven-segment display, is an electronic device that uses seven individual segments to create one digit; it is used in display devices like digital clocks and some basic calculator screens, amongst others.
• In Microsoft's Rich Text Format specification, seven and all numbers congruent to it modulo 256 refer to variants of the German language.
• Windows 7, the upcoming Microsoft operating system sometimes referred to as just "7".
• In the ASCII character set, the bell character.
• There are Seven Tools of Quality.
• There are seven layers in the OSI model.
• There are seven logic gates. NOT, AND, OR, NAND, XOR, NOR, XNOR

In the classical world

In classical antiquity:

• Seven against Thebes
• Seven hills of Rome
• Seven Liberal Arts
• Seven Sages
• Seven Wonders of the ancient world
• Seven emperors (and period; Rome, history):
  • Julius Caesar, Augustus, Galba, Hadrian, Nerva, Sallust, Vespasian

In religion

God rested on and sanctified the seventh day (Shabbat).

• In Judaism:
  • A highly symbolic number in the Torah, alluding to the infusion of spirituality and Godliness into the Creation. For example:
  1. God rested on and sanctified the seventh day (Sabbath).
  2. A seven-day purification period is required for one who has become tamei to become tahor.
  3. The Shemittah (Sabbatical) year arrives every seventh year.
  4. The Jubilee (Yovel) year comes after 7 times 7 years.
  5. The Counting of the Omer leading up to the Giving of the Torah is expressed as "7 times 7 weeks."
  • The weekly Torah portion is divided into seven aliyahs, and seven men or boys over the age of 13 are called up for the reading of these aliyahs during Sabbath morning services.
  • Seven blessings are recited under the chuppah during a Jewish wedding ceremony.
  • David was the eighth son of Jesse.
  • A Jewish bride and groom are feted with seven days of festive meals after their wedding, known as Sheva Berachot ("Seven Blessings").
  • The number of Ushpizzin (also known as the "Seven Shepherds") who visit the sukkah during the holiday of Sukkot: Abraham, Isaac, Jacob, Joseph, Moses, Aaron, and David.
  • The number of nations God told the Israelites they would displace when they entered the land of Israel (Deut. 7:1): the Hittite, the Girgashite, the Amorite, the Canaanite, the Perizzite, the Hivite, and the Jebusite.
  • In Breslov tradition, the seven orifices of the face (2 eyes, 2 nostrils, 2 ears, and the mouth) are called "The Seven Candles."
  • The menorah (Hebrew: מנורה), is a seven branched candelabrum lit by olive oil in the Tabernacle and the Temple in Jerusalem. The menorah is one of the oldest symbols of the Jewish people. It is said to symbolize the burning bush as seen by Moses on Mount Sinai (Exodus 25).
  • On the 7th day of the 7th month of 1947, European Jews began the boarding the ship Exodus in France to return to Israel.^{[citation needed]}

• In Christianity:
  • Yahweh or Jehovah is the divine name, whose letters' places alphabetically equal 70, a product of the divine number 7.
  • The number of churches of Asia to which the "Book of Revelation" is addressed.
  • The number of the Seven Virtues: Chastity, Moderation, Liberality, Charity, Meekness, Zeal, and Humility, corresponding to the seven deadly sins.
  • Jesus told Peter that he should forgive someone who sinned against him 70 times 7 times.
  • The seven terraces of Mount Purgatory (one per deadly sin).
  • The number of sacraments in the Roman Catholic faith.
  • The number of heads of the three beasts [[7*10*7+7*10*10+7*10=1260]] of the Book of Revelation, and of some other monsters, like the hydra and the number of seals.
  • In the New Testament, the Gospel of Matthew 18:21, Jesus says to Peter to forgive seventy times seven times.^[2]
  • The number of times Cain will be avenged by God if he is murdered (Gen 4:15).
  • In Roman Catholicism, and some reformed traditions, the Blessed Virgin Mary has Seven Joys: The Incarnation, the Visitation, the Nativity, the Visit of the Magi, the Finding of Jesus in the Temple of Jerusalem, the Resurrection of Christ, and The Assumption of Mary into Heaven.
  • In Roman Catholicism, and some reformed traditions, the Blessed Virgin Mary has Seven Sorrows: The Prophecy of Simeon, the Flight into Egypt, the Three Day Loss of the Christ Child in the Temple of Jerusalem, the Carrying of the Cross, the Crucifixion of Christ, the Pieta, and the Closing of the Holy Sepulchre.
  • In the genealogy in the Gospel of Luke, Jesus is 77th in a direct line.
  • The Isrealites circled Jericho for 7 days and then the wall tumbled down.

• In Islam:
  • The number of ayat in surat al-Fatiha.
  • The number of heavens in Islamic tradition.
  • The number of Earths in Islamic tradition.
  • The number of circumambulations (Tawaf) that are made around the Kaaba
  • The number of walks {Al-Safa and Al-Marwah) that is travelling back and forth seven times during the ritual pilgrimages of Hajj and Umrah.

• In Eternalism:
  • The number of deities
  • The years Godzimir was exiled to Turin, in Savoy
  • 1/7 of each of the Deities powers was taken to create the Eternal
  • There are seven verses in each of the Septrains of the Prognostications of Godzimir and Invomandus
  • Seven universe in each phase toward Edication

• Others:
  • The number of Archangels according to some systems.
  • The minor symbol number of yang from the Taoist yin-yang.
  • The number of palms in an Egyptian Sacred Cubit.
  • The number of ranks in Mithraism.
  • The number seven is of particular significance within Cherokee cosmology.
  • In Buddhism, Buddha walked 7 steps at his birth.

• In Hinduism:
  • The Sanskrit word 'sapta' refers to number seven.
  • The Indian Music has 'sapta swaras', means seven octats (sa re ga ma pa dha ni), which are basics of music, using which hundreds of Ragas are composed.
  • The Month 'September' is evolved from the word 'septa' meaning seven. September was earlier seventh month before July and August were added to the calendar. Also the subsequent months names are derived from Sanskrit names 'Ashta' and 'Nava' meaning eight and nine which are now called October and November.
  • Celestial group of seven stars are named as 'Sapta Rishi' based on the seven great saints.
  • Seven Promises, Seven Rounds in Hindu Wedding and Seven Reincarnation
  • As per Hindu mythology, there are seven worlds in the universe, seven seas in the world and seven Rishies (seven gurus) called sapta rishis.

In mythology

• In Khasi mythology, the seven divine women who were left behind on earth and became the ancestresses of all humankind.
• The number of gateways traversed by Inanna during her descent into the underworld.
• The number of sleeping men in the Christian myth of the "Seven Sleepers."
• The number of sages in Hindu mythology; their wives are the goddesses referred to as the "Seven Mothers."
• The number of main islands of mythological Atlantis.
• In Guaraní mythology, the number of prominent legendary monsters.
• Seven Lucky Gods exist in Japanese mythology.
• In British Folk lore, every 7 years the Fairy Queen pays a tithe to Hell (or possibly Hel) in the tale of Tam Lin.
• In the British Folk tale of Thomas the Rhymer, he went to live in the faerie kingdom for 7 years.

In psychology

• The Magical Number Seven, Plus or Minus Two is a 1956 paper by cognitive psychologist George Miller, who found a correlation between various human cognitive capacity limits within the range 7±2.

In music

• Song by Prince
• 90's pop band S Club 7
• The number of notes in the traditional Western Major Scale
• The original diameter in inches of the 45rpm format gramophone record.
• In music, the Roman numeral vii is the leading tone (vii°) or subtonic (VII) scale degree, chord, or diatonic function, when distinguished V = major and v = minor.
• The number of completed, numbered symphonies of Jean Sibelius and Sergei Prokofiev.
• A pop music singer in South Korea: SE7EN (singer).
• The "Unsquare Dance" by Dave Brubeck is in septuple meter--seven beats to a measure.
• There are seven musicians in a septet.
• The stage name of musician Keith Volpone.
• The name of one of Jurassic 5's band member, Mark 7even.
• Several bands have the number 7 in their name, and several albums and songs have the number in their title. To give just two examples: the band Avenged Sevenfold released an album in 1999 titled Sounding the Seventh Trumpet, in 1970, Shocking Blue released the song "Seven is a Number in Magic."
• 7 Shades of Black is a song on the Smashing Pumpkins album Zeitgeist, which made it's release in 2007.
• Slipkot Member Mick Tompson Is "Mr.7" and The other band Members have there own Identification Numbers
• Singer, songwriter, actor, and rapper Andre 3000 and Erykah Badu named his first child Seven.
• Christian band "Seventh day slumber"
• Tupac Shakur released The 7 Day Theory under the alias Makaveli in 1996. The first album after his death.
• An album by Enrique Iglesias.

In television

• The name of one of the monsters in the cartoon television show Seven Little Monsters.
• Seven, an episodic character from the sitcom Married... with Children.
• In Star Trek: Voyager, Seven of Nine (also called Seven for short) is one of the crewmembers.
• In an episode of Seinfeld entitled "The Seven", the name George Costanza desired to give his first-born (with Susan Ross) is "Seven;" he later falsely claimed that he had promised this to the widow of baseball great Mickey Mantle, whose uniform number was 7.
• The name of a television show 7th Heaven.
• Seven Network, a television network in Australia.
• Maximum number of VHF broadcast channels available in any TV market in the United States of America; they are channels 2, 4, 5, 7, 9, 11, and 13 in the Greater New York City and Los Angeles-Long Beach SMSAs.
• In Stargate SG-1 and Stargate Atlantis, most gate addresses use 7 chevrons on the gate.
• Ultra Seven, a television series aired in 1967, and the superhero of the same name. He is the honorary seventh member of the Ultra Garrison.
• The name of a memorable The Adventures of Super Mario Bros. 3 cartoon, 7 Continents for 7 Koopas.

In film

• The musical film Seven Brides for Seven Brothers.
• The Marilyn Monroe film The Seven Year Itch which is famous for the white dress blowing up.
• The film Se7en, directed in 1995 by David Fincher and starring Brad Pitt and Morgan Freeman.
• James Bond's agent secret number is 007.
• In the Disney film Snow White and the Seven Dwarfs.
• The film Lucky number s7evin, directed in 2006 by Paul McGuigan.
• The film The Magnificent Seven starring Yul Brynner.
• The Japanese film Seven Samurai directed by Akira Kurosawa.
• The Swedish film The Seventh Seal directed by Ingmar Bergman.
• In 2001: A Space Odyssey (film), Dave Bowman encounters seven octahedra during his journey through the infinite.
• The film Seven Sinners 1940 directed by Tay Garnett, starring Marlene Dietrich

In literature

• In the Harry Potter series of novels by J. K. Rowling, seven is said to be the most powerfully magical number. There are a number of references to seven in Harry Potter: There are a total of seven books in the series; Ginny Weasley is the seventh child and only daughter; Harry Potter was born in July, the seventh month of the year; Wizarding students must complete seven years of school at Hogwarts; Lord Voldemort splits his soul into seven parts which he believes ensures his immortality. Seven is also the number on the back of Harry Potter's Quidditch robes (Prisoner of Azkaban movie). In Quidditch each team consists of seven players. Chapter four of Book 7 is titled "The Seven Potters".
• In The Two Towers, the second volume of J. R. R. Tolkien's The Lord of the Rings, the following poem appears: "Tall ships and tall kings/Three times three/What brought they from the foundered land/Over the flowing sea?/Seven stars and seven stones/And one white tree." The "foundered land" is Númenor, and the "Seven Stars" are unknown, but they may refer to a constellation, the Sickle of the Valar. The Seven Stones are the palantíri, the seeing-stones. Also in The Lord of the Rings, the Dwarves were given seven rings.
• In The Silmarillion, also a Tolkien work, there are seven Lords of the Valar, and seven Ladies of the Valar; Fëanor, a central character, has seven sons: Maedhros, Maglor, Celegorm, Curufin, Caranthir, Amrod, and Amras.
• In Galician folklore, a seventh son will be a werewolf. In other folklores, after six daughters, the seventh child is to be a son and a werewolf. In other European folklores, the seventh son of a seventh son will be a child with special powers of healing and clairvoyant seeing.
• In Fist of the North Star (Hokuto no Ken), the main character, Kenshiro, is also known as "the man with seven wounds" for the seven scars on his body in the shape of the Big Dipper.
• Aleksis Kivi's "Seven Brothers", the most famous book of Finnish literature.
• Seven Pillars of Wisdom, a book written by T. E. Lawrence.
• The Secret Seven, name of achildren's adventure book by Enid Blyton.
• The book Seven Years in Tibet.
• The anime Eureka Seven.
• The character 7 (Nana) and the organisation Septimal Moon in Loveless (manga).
• The Seven Habits of Highly Effective People, a book by Stephen Covey.
• Team 7 consists of the main characters in Naruto: Naruto Uzumaki, Sasuke Uchiha, Kakashi Hatake, and Sakura Haruno.
• In the One Piece series, the Shichibukai (literally, "Seven Military Seas", known in the English versions as the "Seven Warlords of the Sea") are seven powerful pirates who work for the government.
• In the Dragon Ball series, there are 7 Dragon Balls that can grant any wish.
• In the InuYasha series, the Shichinintai are, as their name says, a band of seven mercenaries.
• In the Nana series, there are many recurrent instances of the number seven ("nana" is the Japanese numeral for the English "seven"), including the name of both main characters.
• In George R. R. Martin's A Song of Ice and Fire, seven gods, the Mother, the Father, the Warrior, the Crone, the Smith, the Maiden, and the Stranger, are worshipped in the land of Westeros. The Seven are the primary deities of Westeros.
• In The Dark Tower series by Stephen King there are 7 books.
• In The Wheel of Time series by Robert Jordan, there are 7 seals on the Dark One's prison.

In video games

• 7 is a number used many times by Bungie Studios in their Halo and Marathon games. 7 appears in a variety of different contexts, from the stories of the games to the raw game coding. One obvious example is the fact that there are seven Halo rings strewn throughout the galaxy.
• Final Fantasy VII has many instances of seven throughout the game and was even released (in North America) on the seventh day of September ("September" originally meant "seventh month") in 1997.
• In the Sonic the Hedgehog games, Sonic collects seven Chaos Emeralds (after completing special stages) which, after getting all of them and then collecting at least 50 rings, allow him to turn into Super Sonic. This transformation makes him glow golden yellow and allows him to move at speeds much faster than he already moves (at the speed of sound^[3]). Sonic 3 & Knuckles allows for an even more powerful transformation called 'Hyper Sonic' once an additional seven 'Super Emeralds' are collected.
• The number of individual personalities serving Harman Smith as part of the group of assassins called the Killer7, hence the title of the game.
• In Kingdom Hearts there are seven Princesses of Heart.
• In the Super Mario RPG/Paper Mario series of games, the collection of seven mystical items (predominantly stars, but also hearts in Super Paper Mario) is the main quest of the game.
• In The Legend of Zelda: Ocarina of Time, the main quest involves awakening the seven sages of seven elements to banish evil from the land of Hyrule.
• The number of Koopalings on Super Mario Bros. 3 and Super Mario World. It is also the number of worlds on Super Mario World, not counting the Star World or the Special course; and it is also the number of worlds on Super Mario Bros. 2.
• The 7 is a group of deadly mercenaries that kidnap the protagonist's family in the upcoming video game Kane & Lynch: Dead Men.

In sports

• In Ultimate Frisbee, the number of players on the field for each team.
• In team handball, the number of players on each team including the goalkeeper.
• In rugby league, the scrum-half/halfback.
• In rugby union, the openside flanker.
• In Cricket, the squad number of England's Ian Bell.
• In scoring baseball, seven represents the left fielder's position.
• In baseball, the 7th Inning stretch attributed to the 27th US President, William Howard Taft.
• In high-school baseball a regulation game lasts seven innings.
• Seven Cycles, a bicycle manufacturer
• Retired baseball jersey number of Mickey Mantle.
• Retired football jersey number of Hall of Famer John Elway.
• Retired hockey jersey number of Bill Barber, Phil Esposito, Rod Gilbert and Howie Morenz.
• In the NHL, MLB, and NBA, the maximum number of games played in a playoff series.
• Jersey number of NFL star Ben Roethlisberger.
• Jersey number of Major League Baseball player Jose Reyes and Craig Biggio.
• In the NASCAR NEXTEL Cup, number 7 was used by Alan Kulwicki for his 1992 championship. Number 7 is currently used by Robby Gordon, and number 07 is Clint Bowyer's number.
• Danica Patrick's number in the Indy Racing League.
• Rugby Sevens, a variant of rugby union and rugby league that contains only seven players per side instead of the standard 15 (union) or 13 (league).
• The Rugby World Cup Sevens, the World Cup for the union version of Sevens.
• The IRB Sevens World Series, also in the union version of Sevens.
• Seven, gimmick briefly used by professional wrestler, Virgil Runnels III in World Championship Wrestling.
• In the Harry Potter Series by J.K. Rowling, there are 7 players on a standard Quidditch team.
• Jersey number of Jermaine O'Neal, Brandon Roy, Penny Hardaway, and ex-England captain turned part time celebrity footballer David Beckham.

In other fields