7 (number)

Encyclopedia : 7 : 7N : 7NU : 7 (number)

This article is about the number seven. For other uses, see 7.


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	[[Wiktionary:hepta->hepta-]]/[[Wiktionary:hept-\|hept-]] (from Greek) [[Wiktionary:septua-\|septua-]] (from Latin)
Binary	111
Octal	7
Duodecimal	7
Hexadecimal	7
Hebrew	ז (Zayin)

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

In mathematics

Seven is the fourth 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 nonzero squares.
Seven is a 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.

# Remove the last digit,

# Double it, and

# Subtract it from the remaining digits.

# If the result is negative and there are 2 or more digits, drop the negative sign.

# 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 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

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

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

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

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. 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 7 is written as in ①　in　Japan,Korea and so on.

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

In science

The number of spots in a common ladybug.

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

Astronomy

The number of 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. The seven days of the week were named after these celestial bodies: (Sunday – the Sun's day; Monday – the Moon's day; Tuesday – Mars' day; Wednesday – Mercury's day; Thursday – Jupiter's day; Friday – Venus' day; and Saturday – Saturn's day
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 number of saints appear in a constellation called "Saptharishi Mandalam" in Indian astronomy.
The number of stars in ursa major constellation.
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.

In religion

A highly symbolic number in the Torah, alluding to the infusion of spirituality and Godliness into the Creation. For example:

God rested on and sanctified the 7th day (Shabbat)
A seven-day purification period is required for one who has become tamei to become tahor
The Shemittah (Sabbatical) year arrives every 7th year
The Jubilee (Yovel) year comes after 7 times 7 years
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 Shabbat morning services

Seven blessings are recited under the chuppah during a Jewish wedding ceremony

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 number of churches of Asia to which the Book of Revelation is addressed

The number of ayat in surat al-Fatiha

The number of heavens in Islamic tradition

The number of Earths in Islamic tradition

The numbers 7, 70, 70,000, etc. are used in Islamic traditions to denote an infinite or high number. In Arabic, 70, 70,000, etc. is used to mean infinite. This is because 1 is the smallest number, 2 is just after 1, 5 and 10 are exact, 4 and 6 are just before and after 5, and 9 is just before 10. This leaves 3, 7, and 8. 8 is closer to the end although it is larger. 8 is also an even number, so divisible by 2. Between 3 and 7, 3 is smaller so 7 is chosen to represent infinite.

The number of Seven Virtues: Chastity, Abstinence, Diligence, Liberality, Patience, Kindness, and Humility, and the corresponding Seven 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

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

The number of ranks in Mithraism

The number seven is of particular significance within Cherokee cosmology

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"

In psychology

The Magical Number Seven, Plus or Minus Two is the title of a 1956 paper by the cognitive psychologist George A. Miller which hypothesises that the effective channel capacity of human senses is equivalent to between 5 and 9 equally-weighted error-less choices.
When asked to choose a number between 1 and 10, most people will choose 7. It is the most common number thought of off the top of one's head.

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 ; SE7EN (singer)
A five-piece teenybopper band from the late 1980s.

Albums

A 2004 album by The Tea Party: see Seven circles (Tea Party album.
A 2003 album by Atmosphere: see Seven's Travels.
A 2003 album by Enrique Iglesias: see 7 (Enrique Iglesias album).
A 2002 EP by U2: see 7 (EP).
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 1974 album by Poco.
A 1974 album by Bob Seger: see Seven (Bob Seger album).

A 1991 album by Mannheim Steamroller: see Fresh Aire 7
The album Seventh Son of a Seventh Son by Iron Maiden, based on a book with the same name written by Orson Scott Card.
The 1996 album [[The Don Killuminati: The 7-Day Theory]] by Tupac Shakur.

Songs

The song "Seven" by David Bowie
The song "Seven" by Sunny Day Real Estate
The song "Seven" by Gackt
The song "Seven by Necrophagist
The song "7" by Prince
The short instrumental piece "7" by Moby
The song "Seven Nation Army" by The White Stripes
The song "Seven Seas Of Rhye" by Queen
The song "Song Seven" by Interpol

In sports

In rugby league, the scrum-half/halfback
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.
Seven Cycles, a bicycle manufacturer
Number of John Elway, Hall of Fame QB of the Denver Broncos.
Number associated with England National Team captain, David Beckham.

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). 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 ASCII character set, the bell character

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.
7 is the number of hearts needed by the gentlemen in "Buffy the Vampire Slayer" during the episode known to as "hush".
In [[Star Trek: Voyager]], Seven of Nine (also called Seven for short) is one of the crewmembers.

In film

The film Se7en, directed in 1995 by David Fincher.
In the Disney film Herbie Goes to Monte Carlo (1977), the car number of Giselle, the Lancia Scorpion with whom Herbie falls in love.
James Bond's agent secret number is 007.

In other fields

Seven candles are lit in the kinara during the African-American celebration of Kwanzaa, which is a seven-day holiday
It is traditionally thought that there are seven continents on Earth.
Seven is the smallest positive integer requiring more than one syllable 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 have been built on seven hills.
Serial sevens are used as a diagnostic test in medicine.
In linguistics, the "7" is sometimes used to represent a glottal stop, as a substitute for ʔ.
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.
The Harry Potter series has several references to the number seven.

Seven is also:

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 (mouth, two eyes, two ears, two nostrils).
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 both Japanese Culture and many Western cultures.
The number of days in a week. Whether Saturday or Sunday is the seventh day varies across cultures.
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 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 vampire.
When rolling two standard six-sided dice, seven is the number most likely to occur.
Seven is the sum of any two opposite sides on a standard six-sided die
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 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
The traditional count of Basque provinces as expressed in the slogan Zazpiak Bat
The Seven Sages of Greece: Solon, Chilon, Thales, Bias, Cleobulus, Pittacus and Periander.
Cibola was the legendary Seven Cities of Gold the Spanish thought existed.
In tarot, card No. 7 is "the Chariot"

Names and titles

Seven or 7 is all or part of a number of names and titles of people, artworks or organizations, including:

Sevens, a card game
An agency of photojournalists founded by seven photographers
Canadian fashion photographer Sev Seven
Musician/actor Andre Benjamin's and singer Erykah Badu's son, Seven.
The stage name of musician Keith Volpone
SE7EN (singer), a Korean R&B/hip-hop singer
Part of the names of:
* 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 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
* Several groupings called the Seven Sisters
*The Anime Eureka Seven
* 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
* Seven of Nine, a crewmember 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 single by the White Stripes
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.
In the Fushigi Yuugi series, the four beast gods each have seven warriors. The Genbu Seven, the Byakko Seven, the Seiryuu Seven, and the Suzaku Seven.
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 the catalan culture, 7 is present in a lot of popular stories like "Les set cabretes i el llop".

Historical years

A.D. 7, 7 B.C., 1907, 2007, etc.