# 7 number

 0 10 20 30 40 50 60 70 80 90 >> 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)

For the 1995 American murder thriller movie, go to Se7en.

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).

## In mathematics

Seven is the fourth-smallest prime number; the next is 11. Seven is a Mersenne prime, since 23 - 1 = 7. Seven is also the fourth Mersenne prime exponent, the first Newman-Shanks-Williams prime, the third Lucas prime, and the first Woodall prime. 7 is also the second lucky prime, the second safe prime, and the fourth factorial prime. 7 is the smallest number that can't be represented as a sum of fewer than four nonzero squares. 7 is also a self number.

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

BaseNumeral system
2binary 111
3ternary 21
4quaternary 13
5quinary 12
6senary 11
7septenary 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, File:TextFigs078.png.

## In science

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

### Albums

There are several albums titled 7:

## In other fields

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 name of an elite agency of photojournalists founded by seven leading photographers, including James Nachtwey and others

• The number of "Zoomers" on the PBS children's show Zoom
• The traditional count of Basque provinces as expressed in the slogan Zazpiak Bat
• 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.
• Sevens is a card game
• 007, codename for James Bond, a fictional secret spy agent
• 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.
• In the Inuyasha series, the Shichinintai are, as their name says, a band of seven mercenaries.
• Historical years: A.D. 7, 7 B.C., or 1907