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Cardinal	7 seven
Ordinal	7th seventh
Numeral system	septenary
Factorization	prime
Divisors	1, 7
Roman numeral	VII
Unicode representation of Roman numeral	Ⅶ, ⅶ
prefixes	hepta-/hept- (from Greek) septua- (from Latin)
Binary	111
Octal	7
Duodecimal	7
Hexadecimal	7
Hebrew	ז (Zayin)

This article is about the number seven. For the 1995 American murder thriller movie, go to Seven (film). For the Australian television network, go to Seven Network

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

The SI prefix for 1000⁷ is zetta (Z), and for its reciprocal zepto (z).

Contents 1 In mathematics 1.1 In numeral systems 2 The Arabic glyph 3 In science 4 Language 5 In music 5.1 Albums 6 In religion 7 In sports 8 In technology 9 In television 10 In other fields 10.1 Names 11 See also

In mathematics

• Seven is the fourth-smallest prime number; the next is 11.
• 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 also the second lucky prime.
• Seven is the second safe prime.
• Seven is the fourth factorial prime
• Seven is the smallest number that can't be represented as a sum of fewer than four nonzero squares.
• Seven is also a self number.

• 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. 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 easy, once we rewrite the number n 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)

• 999,999 divided by 7 is exactly 142,857, so vulgar fractions with 7 in the denominator have six-digit repeating sequences in their decimal expansions. 1/7 = 0.142857142....

• A seven-sided polygon is a heptagon. The regular n-gons for n ≤ 6 can be constructed by ruler and compass 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

Base	Numeral system
2	binary	111
3	ternary	21
4	quaternary	13
5	quinary	12
6	senary	11
7	septenary	10
over 7 (octal, decimal)		7

The Arabic 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, and so they were also concerned with making their 7 more different. For the Khmer this often involved adding a horizontal line above the glyph. 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.

On the seven-segment displays of pocket calculators and digital watches, 7 is the number with the most common glyph variation (0 and 6 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.

In fonts with text figures, 7 usually has a descender, for example, .

In science

• 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.
• The neutral pH - the pH level of pure water

In astronomy,

The number of objects in the solar system visible to the naked eye, the classical "planets" (Moon, Mars, Mercury, Jupiter, Venus, Saturn, Sun). A fact that is believed to have led to the concept of seven days of the week.

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 seven daughters of Atlas in the Pleiades (also called the "seven sisters").

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 1280.1 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 1586.6 years, and it contained 89 lunar eclipses.

Language

In Cantonese, the 16th most popular language in the world, the number 7 is pronounced exactly like the word for the male genitalia. It is coined for the negative phrase "You are 7", which has a slightly different meaning to "You are the male genitalia". It is very popular among teens.

In music

• The number of notes in the musical scale
• In music, the Roman numeral vii is the subtonic (bVII) or leading tone (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. (세븐)

Albums

There are several albums titled 7:

• A 2003 album by Enrique Iglesias: see 7 (Enrique Iglesias album).
• A 2000 album by S Club 7: see 7 (S Club 7 album)
• A 1997 album by Zap Mama: see 7 (Zap Mama album)
• A 1996 album by Apoptygma Berzerk: see 7 (Apoptygma Berzerk album)
• A 1992 album by James: see Seven (James album).
• A 1986 album by George Strait: see 7 (George Strait album)
• A 1985 album by David Meece: see 7 (David Meece album)
• A 1981 album by Madness: see 7 (Madness album)
• A 1991 album by Mannheim Steamroller: see Fresh Aire 7

In religion

• A highly symbolic number in the Hebrew Bible, being, for example, the day on which God rested in Genesis
• The number of ayat in surat al-Fatiha
• The number of heavens in Islamic tradition
• The number of the Deadly Sins: lust, avarice, envy, pride, sloth, gluttony and wrath
• The seven terraces of Mount Purgatory (one per deadly sin)
• The number of sacraments in the Roman Catholic faith
• Considered the usual number for a witches' coven
• The number of palms in an Egyptian Sacred Cubit
• The number of heads of the beast of the book of Revelation, and of some other monsters, like the hydra
• The minor symbol number of yang from the Taoist yin-yang.
• The number of times Cain will be avenged upon for the murder of his brother Abel.

In sports

• In rugby union, the openside flanker
• In baseball, seven represents the left fielder's position
• Retired jersey number of former baseball player Mickey Mantle and former hockey player Ted Lindsay.
• Boomer Esiason's jersey number

In technology

• The code for international direct dial phone calls to Russia and Kazakhstan
• On most phones, the 7 key is associated with the letters P, R, and S (there are a few phones that also put Q on 7, such as Sony Ericson cell phones), but on the BlackBerry it is the key for C and V.
• The number of digits in an American telephone number, excluding the area code
• The number of individual segments in one digit on a digital clock or calculator seven-segment display screen
• In all Microsoft Office programs, the F7 function key calls up the spelling and grammar checker
• In most Sonic the Hedgehog video games, the number of Chaos Emeralds
• In ASCII character set, the bell character
• The letter T in the computer language "leet" (1337)

In television

• In an episode of Seinfeld, the name George Costanza desired to give his first-born (with Susan Ross) due to a promise he had made to the widow of Mickey Mantle, whose number was 7
• The name of one of the monsters in the cartoon television show Seven Little Monsters
• A character added to the cast of Married... with Children who was quickly removed.

In other fields

• Historical years: A.D. 7, 7 B.C., or 1907

• There are seven continents on Planet Earth.

• Seven is the smallest positive integer requiring two syllables in English.

• There are seven musicians in a septet and seven babies born in a set of septuplets. The most famous set of septuplets are the McCaughey Septuplets, who were born in 1997.

• The British fifty-pence and twenty-pence coins are heptagons, with the sides curved to give them a constant diameter.

• Many cities are claimed to be constructed amidst seven hills; see Seven hills of Rome and List of cities claimed to be built on seven hills.

• Serial sevens are used as a diagnostic test in medicine.

Seven is also:

• The maximum amount of times that you can fold a sheet of paper in half
• The largest number of sticks (or other cylindrical objects) that can be tied into a bundle such that the shape of the bundle remains fixed. This may have led to the number being viewed with mystical significance by ancient man.
• The number of openings into the human head.
• The number of spheres in the Ptolemaic system
• In Astrology, Libra is the 7th astrological sign of the Zodiac.
• The traditional number of Wonders of the Ancient World.
• Viewed as a lucky number in many Western cultures, and in Japanese culture.
• The number of days in a week. Whether Saturday or Sunday is the seventh day varies across cultures.
• Referred to in bingo as 'Lucky Seven'
• The number of the ages of man into which William Shakespeare divided a lifetime
• The figurative number of seas
• The number of colors of the rainbow (the asteroid 7 Iris is named after the rainbow goddess Iris)
• The number of basic principles of the bushido
• The number of points on a sheriff's star
• The average number of digits that can be stored in short-term memory
• In the movie The Ring, the number of days until you die, after watching The Cursed Videotape.
• In Galician folklore, the 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 vampire.
• When rolling two standard six-sided dice, you are statistically more likely to roll a seven than any other number
• In the Sailor Moon cartoon, the characters must find the seven Nijizuishou.
• Seven is the sum of any two opposite sides on a standard six-sided die
• In the Harry Potter series, seven is considered to be the most magically powerful number. Lord Voldemort is suspected to have split his soul into seven pieces.
• Many Bungie games directly and indirectly reference the number seven often. For example, the UESC Marathon from the self-titled game series was built by hollowing out Deimos, a moon discovered in 1877.
• The number of dwarves in the movie Snow White
• The number of rings given to the Dwarf Lords in J.R.R. Tolkien's The Lord of the Rings
• The number of "Zoomers" on the PBS children's show Zoom
• Aleksis Kivi's masterpiece "The seven Brothers" is the most famous book of Finnish literature

Names

• The Heptarchy, from the (Greek for seven realm, is the name applied by historians to the period (500-850 AD) in English history after the Anglo-Saxon conquest of England, derived from the seven kingdoms of Northumbria, Mercia, East Anglia, Essex, Kent, Sussex, and Wessex, which eventually merged to become the Kingdom of England during the early 10th century.

• September was the seventh month in the ancient Roman calendar, as its name indicates. After the reform that led to the current order, the seventh month is July.

• Septidi was the seventh day of the decade in the French Revolutionary Calendar

Seven is:

• The name of an elite agency of photojournalists founded by seven leading photographers, including James Nachtwey and others
• The name of musician/actor Andre Benjamin's and singer Erykah Badu's son, Seven.
• The stage name of musician Keith Volpone

• The title of:
  • The film Seven (or Se7en), directed in 1995 by David Fincher and starring Morgan Freeman, Brad Pitt and Kevin Spacey
  • The album and song Seventh Son of a Seventh Son by Iron Maiden, also based on a book with the same name written by Orson Scott Card.
  • The song "Seven" by David Bowie

• Part of the names of:
  • Seven Pillars of Wisdom, a book written by T. E. Lawrence
  • The Secret Seven, name of children adventure book by Enid Blyton
  • The book Seven Years in Tibet
  • Kurosawa's film The Seven Samurai, that inspired the 1960 movie with Steve McQueen The Magnificent Seven and its own sequels
  • The video game Final Fantasy VII
  • Several groupings called the Seven Sisters
  • The Seven Virgins:
    • The Seven Virgins mountain range in Sri Lanka, which was the scene of an air disaster on 4 December 1974, involving a DC-8 Series 55F passenger jetliner operated by the charter company Martinair which left 191 dead.
    • the Saptha Kanniyar were seven faithful devotees of Siva, who give birth to seven boys, in Hindu mythology.
    • An anonymous 17th Century carol, The Seven Virgins.
  • Seven Sisters, a 1998 song album by pop singer Meja
  • The crewmember, Seven of Nine, in the Star Trek universe
  • The World Sevens Series in Rugby Union, including the Hong Kong Sevens
  • the sport itself
  • The Seven Network of Australia
  • The Seven Habits of Highly Effective People, a book by Stephen Covey
  • The metal band Avenged Sevenfold, also known as A7X.
  • "Seven Nation Army," a popular single by the White Stripes
  • The Seven Sages of Greece: Solon, Chilon, Thales, Bias, Cleobulus, Pittacus and Periander.
• The traditional count of Basque provinces as expressed in the slogan Zazpiak Bat
• Sevens is a card game
• 007, codename for James Bond, a fictional secret spy agent
• In the InuYasha series, the Shichinintai are, as their name says, a band of seven mercenaries.

See also

• Septenary (Theosophy)
• Seven climes
• Seven Seas

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