7 (seven) is the
natural number following
6 and preceding
8. It is the only
prime number preceding a
cube
In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex. Viewed from a corner it is a hexagon and its net is usually depicted as a cross.
The cube is the only r ...
.
As an early
prime number in the series of
positive integers, the number seven has greatly symbolic associations in
religion,
mythology,
superstition
A superstition is any belief or practice considered by non-practitioners to be irrational or supernatural, attributed to fate or magic, perceived supernatural influence, or fear of that which is unknown. It is commonly applied to beliefs and ...
and
philosophy
Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. Some ...
. The seven
Classical planets resulted in seven being the number of days in a week. It is often considered
lucky in
Western culture and is often seen as
highly symbolic. Unlike
Western culture, in
Vietnamese culture, the number seven is sometimes considered unlucky.
It is the first natural number whose pronunciation contains more than one syllable.
Evolution of the Arabic digit
In the
beginning, Indians wrote 7 more or less in one stroke as a curve that looks like an uppercase vertically inverted. The western Ghubar Arabs' main contribution was to make the longer line diagonal rather than straight, though they showed some tendencies to making the digit more rectilinear. The eastern
Arabs developed the digit from a form that looked something like our 6 to one that looked like an uppercase V. Both modern Arab forms influenced the European form, a two-stroke form consisting of a horizontal upper stroke joined at its right to a stroke going down to the bottom left corner, a line that is slightly curved in some font variants. As is the case with the
European digit, the Cham and Khmer digit for 7 also evolved to look like their digit 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 to the top of the digit. 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
1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of ''unit length'' is a line segment of length 1. I ...
in writing that uses a long upstroke in the glyph for 1. In some Greek dialects of the early 12th century the longer line diagonal was drawn in a rather semicircular transverse line.
On the
seven-segment displays of pocket calculators and digital watches, 7 is the digit with the most common graphic variation (1, 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 because in Japan, Korea and Taiwan 7 is written with a "hook" on the left, as ① in the following illustration.
While the shape of the character for the digit 7 has an
ascender in most modern
typefaces, in typefaces with
text figures the character usually has a
descender, as, for example, in
.
Most people in Continental Europe, and some in Britain and Ireland as well as Latin America, write 7 with a line in the middle ("
7"), sometimes with the top line crooked. The line through the middle is useful to clearly differentiate the digit from the digit one, as the two can appear similar when written in certain styles of handwriting. This form is used in official handwriting rules for primary school in Russia, Ukraine, Bulgaria, Poland, other Slavic countries, France, Italy, Belgium, Finland, Romania, Germany, Greece, and Hungary.
Mathematics
Seven, the fourth
prime number, is not only a
Mersenne prime (since ) but also a
double Mersenne prime since the exponent, 3, is itself a Mersenne prime. It is also a
Newman–Shanks–Williams prime, a
Woodall prime, a
factorial prime, a
lucky prime, a
happy number (happy prime), a
safe prime (the only ), a
Leyland prime of the second kind and the fourth
Heegner number In number theory, a Heegner number (as termed by Conway and Guy) is a square-free positive integer ''d'' such that the imaginary quadratic field \Q\left sqrt\right/math> has class number 1. Equivalently, its ring of integers has unique factoriza ...
.
*Seven is the lowest natural number that cannot be represented as the sum of the squares of three integers. (See
Lagrange's four-square theorem#Historical development.)
*Seven is the
aliquot sum of one number, the
cubic number and is the base of the 7-aliquot tree.
*7 is the only number ''D'' for which the equation has more than two solutions for ''n'' and ''x'' natural. In particular, the equation is known as the
Ramanujan–Nagell equation.
*7 is the only dimension, besides the familiar 3, in which a vector
cross product
In mathematics, the cross product or vector product (occasionally directed area product, to emphasize its geometric significance) is a binary operation on two vectors in a three-dimensional oriented Euclidean vector space (named here E), and is ...
can
be defined.
*7 is the lowest
dimension of a known
exotic sphere
In an area of mathematics called differential topology, an exotic sphere is a differentiable manifold ''M'' that is homeomorphic but not diffeomorphic to the standard Euclidean ''n''-sphere. That is, ''M'' is a sphere from the point of view of al ...
, although there may exist as yet unknown exotic smooth structures on the 4-dimensional sphere.
* divided by 7 is exactly . Therefore, when a
vulgar fraction with 7 in the
denominator is converted to a
decimal
The decimal numeral system (also called the base-ten positional numeral system and denary or decanary) is the standard system for denoting integer and non-integer numbers. It is the extension to non-integer numbers of the Hindu–Arabic numeral ...
expansion, the result has the same six-
digit
Digit may refer to:
Mathematics and science
* Numerical digit, as used in mathematics or computer science
** Hindu-Arabic numerals, the most common modern representation of numerical digits
* Digit (anatomy), the most distal part of a limb, such ...
repeating sequence after the decimal point, but the sequence can start with any of those six digits. For example, and
:In fact, if one sorts the digits in the number 142,857 in ascending order, 124578, it is possible to know from which of the digits the decimal part of the number is going to begin with. The remainder of dividing any number by 7 will give the position in the sequence 124578 that the decimal part of the resulting number will start. For example, 628 ÷ 7 = ; here 5 is the remainder, and would correspond to number 7 in the ranking of the ascending sequence. So in this case, . Another example, , hence the remainder is 2, and this corresponds to number 2 in the sequence. In this case, .
*A seven-sided shape is a
heptagon. The regular ''n''-gons for ''n'' ≤ 6 can be constructed by
compass and straightedge
In geometry, straightedge-and-compass construction – also known as ruler-and-compass construction, Euclidean construction, or classical construction – is the construction of lengths, angles, and other geometric figures using only an ideali ...
alone, but the regular heptagon cannot.
Figurate numbers representing heptagons (including seven) are called
heptagonal numbers. Seven is also a
centered hexagonal number
In mathematics and combinatorics, a centered hexagonal number, or hex number, is a centered figurate number that represents a hexagon with a dot in the center and all other dots surrounding the center dot in a hexagonal lattice. The following ...
.
*There are seven
frieze groups, the
groups consisting of
symmetries of the plane whose group of
translations is
isomorphic
In mathematics, an isomorphism is a structure-preserving mapping between two structures of the same type that can be reversed by an inverse mapping. Two mathematical structures are isomorphic if an isomorphism exists between them. The word is ...
to the group of
integers.
*There are seven fundamental types of
catastrophes.
*When rolling two standard six-sided
dice
Dice (singular die or dice) are small, throwable objects with marked sides that can rest in multiple positions. They are used for generating random values, commonly as part of tabletop games, including dice games, board games, role-playing g ...
, seven has a 6 in 6 (or ) probability of being rolled (1–6, 6–1, 2–5, 5–2, 3–4, or 4–3), the greatest of any number. The opposite sides of a standard six-sided dice always add to 7.
*The
Millennium Prize Problems
The Millennium Prize Problems are seven well-known complex mathematical problems selected by the Clay Mathematics Institute in 2000. The Clay Institute has pledged a US$1 million prize for the first correct solution to each problem. According t ...
are seven problems in
mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
that were stated by the
Clay Mathematics Institute
The Clay Mathematics Institute (CMI) is a private, non-profit foundation (nonprofit), foundation dedicated to increasing and disseminating mathematics, mathematical knowledge. Formerly based in Peterborough, New Hampshire, the corporate address i ...
in 2000. Currently, six of the problems remain
unsolved.
Basic calculations
In science
* Seven colors in a rainbow:
ROYGBIV
* Seven
Continents
*
Seven Seas
*
Seven climes
* The neutral
pH balance
* Number of music notes in a scale
* Number of spots most commonly found on ladybugs
* Atomic number for
Nitrogen
In Psychology
*
Seven, plus or minus two as a model of
working memory.
* Seven
psychological types called the
Seven Rays in the teachings of
Alice A. Bailey
* In Western Culture, Seven is consistently listed as people's favorite number.
* When guessing numbers 1-10 the number 7 is most likely to be picked.
*
Seven-year itch: happiness in marriage said to decline after 7 years
Classical antiquity
The
Pythagoreans invested particular numbers with unique spiritual properties. The number seven was considered to be particularly interesting because it consisted of the union of the physical (number
4) with the spiritual (number
3). In Pythagorean
numerology
Numerology (also known as arithmancy) is the belief in an occult, divine or mystical relationship between a number and one or more coinciding events. It is also the study of the numerical value, via an alphanumeric system, of the letters in ...
the number 7 means spirituality.
References from classical antiquity to the number seven include:
*Seven
Classical planets and the derivative
Seven Heavens
*
Seven Wonders of the ancient world
*Seven
metals of antiquity
The metals of antiquity are the seven metals which humans had identified and found use for in prehistoric times in Europe and the Middle East: gold, silver, copper, tin, lead, iron, and mercury. These seven are the metals from which the moder ...
*
Seven days in the week
*
Seven Seas
*
Seven Sages
*
Seven champions that fought Thebes
*
Seven hills of Rome and
Seven Kings of Rome
*
Seven Sisters, the daughters of
Atlas also known as the
Pleiades
Religion and mythology
Judaism
The number seven forms a widespread
typological
Typology is the study of types or the systematic classification of the types of something according to their common characteristics. Typology is the act of finding, counting and classification facts with the help of eyes, other senses and logic. Ty ...
pattern within
Hebrew scripture, including:
*Seven days (more precisely
yom) of Creation, leading to the seventh day or
Sabbath
In Abrahamic religions, the Sabbath () or Shabbat (from Hebrew ) is a day set aside for rest and worship. According to the Book of Exodus, the Sabbath is a day of rest on the seventh day, commanded by God to be kept as a holy day of rest, as G ...
(Genesis 1)
*Seven-fold vengeance visited on upon
Cain
Cain ''Káïn''; ar, قابيل/قايين, Qābīl/Qāyīn is a Biblical figure in the Book of Genesis within Abrahamic religions. He is the elder brother of Abel, and the firstborn son of Adam and Eve, the first couple within the Bible. He wa ...
for the killing of
Abel (Genesis 4:15)
*Seven pairs of every clean animal loaded onto the ark by Noah (Genesis 7:2)
*Seven years of plenty and seven years of famine in Pharaoh's dream (Genesis 41)
*Seventh son of Jacob,
Gad, whose name means good luck (Genesis 46:16)
*Seven times bullock's blood is sprinkled before God (Leviticus 4:6)
*Seven nations God told the
Israelites they would displace when they entered the land of
Israel (Deuteronomy 7:1)
*Seven days of the
Passover feast (Exodus 13:3–10)
*Seven-branched
candelabrum
A candelabra (plural candelabras) or candelabrum (plural candelabra or candelabrums) is a candle holder with multiple arms.
Although electricity has relegated candleholders to decorative use, interior designers continue to model light fixtures ...
or
Menorah (Exodus 25)
*Seven
trumpets played by seven priests for seven days to bring down the walls of Jericho (Joshua 6:8)
*Seven things that are detestable to God (Proverbs 6:16–19)
*Seven Pillars of the
House of Wisdom
The House of Wisdom ( ar, بيت الحكمة, Bayt al-Ḥikmah), also known as the Grand Library of Baghdad, refers to either a major Abbasid public academy and intellectual center in Baghdad or to a large private library belonging to the Abba ...
(Proverbs 9:1)
*Seven archangels in the deuterocanonical
Book of Tobit
The Book of Tobit () ''Tōbith'' or ''Tōbit'' ( and spellings are also attested) itself from he, טובי ''Tovi'' "my good"; Book of Tobias in the Vulgate from the Greek ''Tōbias'', itself from the Hebrew ''Tovyah'' " Yah is good", also k ...
(12:15)
References to the number seven in Jewish knowledge and practice include:
*Seven divisions of the weekly readings or
aliyah
Aliyah (, ; he, עֲלִיָּה ''ʿălīyyā'', ) is the immigration of Jews from Jewish diaspora, the diaspora to, historically, the geographical Land of Israel, which is in the modern era chiefly represented by the Israel, State of Israel ...
of the
Torah
*Seven Jewish men (over the age of 13) called to read aliyahs in
Shabbat
Shabbat (, , or ; he, שַׁבָּת, Šabbāṯ, , ) or the Sabbath (), also called Shabbos (, ) by Ashkenazim, is Judaism's day of rest on the seventh day of the week—i.e., Saturday. On this day, religious Jews remember the biblical storie ...
morning services
*Seven blessings recited under the
chuppah during a Jewish wedding ceremony
*Seven days of festive meals for a Jewish bride and groom after their wedding, known as Sheva Berachot or Seven Blessings
*Seven
Ushpizzin prayers to the Jewish patriarchs during the holiday of
Sukkot
or ("Booths, Tabernacles")
, observedby = Jews, Samaritans, a few Protestant denominations, Messianic Jews, Semitic Neopagans
, type = Jewish, Samaritan
, begins = 15th day of Tishrei
, ends = 21st day of Tishre ...
Christianity
Following the traditional of the
Hebrew Bible, the
New Testament likewise uses the number seven as part of a
typological
Typology is the study of types or the systematic classification of the types of something according to their common characteristics. Typology is the act of finding, counting and classification facts with the help of eyes, other senses and logic. Ty ...
pattern:
*Seven loaves
multiplied into seven basketfuls of surplus (Matthew 15:32–37)
*Seven
demons
A demon is a malevolent supernatural entity. Historically, belief in demons, or stories about demons, occurs in religion, occultism, literature, fiction, mythology, and folklore; as well as in media such as comics, video games, movies, anime, ...
were driven out of
Mary Magdalene
Mary Magdalene (sometimes called Mary of Magdala, or simply the Magdalene or the Madeleine) was a woman who, according to the four canonical gospels, traveled with Jesus as one of his followers and was a witness to crucifixion of Jesus, his cru ...
(Luke 8:2)
*
Seven last sayings of Jesus on the cross
*Seven men of honest report, full of the Holy Ghost and wisdom (Acts 6:3)
*
Seven Spirits of God,
Seven Churches
The Seven Churches of Revelation, also known as the Seven Churches of the Apocalypse and the Seven Churches of Asia, are seven major Churches of Early Christianity, as mentioned in the New Testament Book of Revelation. All of them are located in ...
and
Seven Seals in the
Book of Revelation
References to the number seven in Christian knowledge and practice include:
*
Seven Gifts of the Holy Spirit
*
Seven Corporal Acts of Mercy and
Seven Spiritual Acts of Mercy
*
Seven deadly sins: lust, gluttony, greed, sloth, wrath, envy, and pride, and seven terraces of Mount
Purgatory
*
Seven Virtues: chastity, temperance, charity, diligence, kindness, patience, and humility
*
Seven Joys and Our Lady of Sorrows, Seven Sorrows of the Virgin Mary
*Seven Sleepers of Christian myth
*Seven Sacraments in the Catholic Church (though some traditions assign a different number)
Islam
References to the number seven in Islamic knowledge and practice include:
*Seven ayat in surat al-Fatiha, the first book of the holy Qur'an
*Seven Tawaf, circumambulations of Muslim pilgrims around the Kaaba in Mecca during the Hajj and the Umrah
*Seven walks between Al-Safa and Al-Marwah performed Muslim pilgrims during the Hajj and the Umrah
*Seven doors to hell (for heaven the number of doors is eight)
*Seventh day Naming ceremony#Islam, naming ceremony held for babies
*Seven enunciators of divine revelation (''nāṭiqs'') according to the celebrated Fatimid Caliphate, Fatimid Isma'ilism, Ismaili dignitary Nasir Khusraw
*Circle Seven Koran, the holy scripture of the Moorish Science Temple of America
Hinduism
References to the number seven in Hindu knowledge and practice include:
*Seven worlds in the universe and seven seas in the world in Hindu cosmology
*Seven sages or Saptarishi and their seven wives or Sapta Matrka in Hindu mythology
*Seven Chakras in eastern philosophy
*Seven stars in a constellation called "Saptarshi, Saptharishi Mandalam" in Indian astronomy
*Seven promises, or Saptapadi, and seven circumambulations around a fire at Hindu weddings
*Seven virgin goddesses or Saptha Kannimar Padal, Saptha Kannimar worshipped in temples in Tamil Nadu, India
*Seven hills at Tirumala known as Yedu Kondalavadu in Telugu language, Telugu, or ezhu malaiyan in Tamil language, Tamil, meaning "Sevenhills God"
*Seven steps taken by the Buddha at birth
*Seven divine ancestresses of humankind in Khasi people, Khasi mythology
*Seven octets or Saptak Swaras in Indian Music as the basis for Rāga, Ragas compositions
*Seven Social Sins listed by Mahatma Gandhi
Eastern tradition
Other references to the number seven in Eastern traditions include:
*Seven Lucky Gods or gods of good luck, fortune in Japanese mythology
*Seven-Branched Sword in Japanese mythology
*Seven Sages of the Bamboo Grove in China
*Seven minor symbols of yin and yang, yang in Taoist yin-yang
Other references
Other references to the number seven in traditions from around the world include:
*Seven palms in an Egyptian ''cubit, Sacred Cubit''
*Seven ranks in Mithraism
*Seven hills of Istanbul
*Seven islands of Atlantis
*Seven Cherokee clans
*Seven lives of cats in Iran and German language, German and Romance Languages, Romance language-speaking cultures
*Seven fingers on each hand, seven toes on each foot and seven pupils in each eye of the Irish epic hero Cúchulainn
*Seventh sons will be werewolf, werewolves in Galicia (Spain), Galician folklore, or the son of a woman and a werewolf in other European folklores
*Seventh son of a seventh son, Seventh sons of a seventh son will be magicians with special powers of healing and clairvoyance in some cultures, or vampires in others
*Seven prominent Guaraní mythology#Seven legendary monsters, legendary monsters in Guaraní mythology
*Seven gateways traversed by Inanna during her descent into the underworld
*''Seven Wise Masters'', a cycle of medieval stories
*Seven sister goddesses or fates in Baltic mythology called the List of Lithuanian gods and mythological figures#Gods and goddesses, Deivės Valdytojos.
*Seven legendary Cities of Gold, such as Quivira and Cíbola, Cibola, that the Spanish thought existed in South America
*Seven years spent by Thomas the Rhymer in the faerie kingdom in the eponymous British folk tale
*Seven-year cycle in which the Queen of Elphame, Queen of the Fairies pays a tithe to Hell (or possibly Hel (location), Hel) in the tale of Tam Lin
*''Seven Valleys'', a text by the Prophet-Founder Bahá'u'lláh in the Bahá'í faith
*Seven superuniverses in the cosmology of Urantia
*Seven
psychological types called the
Seven Rays in the teachings of
Alice A. Bailey
*The sacred number of Yemaya
Yemaya
Santeria Church of the Orishas. Retrieved 25 November 2022
In culture
In literature
* Seven Dwarfs
* Seven features prominently in ''A Song of Ice and Fire'' by George R. R. Martin, namely, the Seven Kingdoms and the Faith of the Seven
In sports
* Sports with seven players per side
** Kabaddi
** Rugby sevens
** Water Polo
** Netball
** Handball
** Flag Football
** Ultimate Frisbee
* Seven is the least number of players a soccer team must have on the field in order for a match to start and continue.
* A touchdown plus an Conversion (gridiron football), extra point is worth seven points.
See also
*Diatonic scale (7 notes)
*Rainbow, Seven colors in the rainbow
*Seven continents
*Seven liberal arts
*Seven Wonders of the Ancient World
*Seven days of the Week
*Septenary, Septenary (numeral system)
*Year Seven (School)
*Se7en (disambiguation)
*Sevens (disambiguation)
*One-seventh area triangle
* Z with stroke (Ƶ)
*List of highways numbered 7
Notes
References
*Wells, D. ''The Penguin Dictionary of Curious and Interesting Numbers'' London: Penguin Group (1987): 70–71
{{DEFAULTSORT:7 (Number)
Integers
7 (number)