|Roman numeral||VII, vii|
|Greek numeral||Z, ζ|
|Arabic, Kurdish, Persian||٧|
|Chinese numeral||七, 柒|
As an early prime number in the series of positive integers, the number seven has greatly symbolic associations in religion, mythology, superstition and philosophy. 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.
In English, 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 ⟨J⟩ 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 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.
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, the Netherlands, Finland, Romania, Germany, Greece, and Hungary.
Seven, the fourth prime number, is not only a Mersenne prime (since 23 − 1 = 7) 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 Harshad number, a lucky prime, a happy number (happy prime), a safe prime (the only Mersenne safe prime), a Leyland prime of the second kind and the fourth Heegner number.
- 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.)
- 7 is the only number D for which the equation 2n − D = x2 has more than two solutions for n and x natural. In particular, the equation 2n − 7 = x2 is known as the Ramanujan–Nagell equation.
- 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 seven-sided shape is a heptagon. The regular n-gons for n ⩽ 6 can be constructed by compass and straightedge alone, which makes the heptagon the first regular polygon that cannot be directly constructed with these simple tools. Figurate numbers representing heptagons are called heptagonal numbers. 7 is also a centered hexagonal number.
- A heptagon in Euclidean space is unable to generate uniform tilings alongside other polygons, like the regular pentagon. However, it is one of fourteen polygons that can fill a plane-vertex tiling, in its case only alongside a regular triangle and a 42-sided polygon (3.7.42). This is also one of twenty-one such configurations that also features the largest and smallest polygons possible.
- Wythoff's kaleidoscopic constructions use 7 distinct generator points that lie on mirror edges of a three-sided Schwarz triangle to create most uniform tilings and polyhedra; an eighth generator point lying on all three mirrors is technically degenerate and is reserved to represent snub forms only.
- Seven of eight semiregular tilings are Wythoffian, the only exception is the elongated triangular tiling. Seven of nine uniform colorings of the square tiling are also Wythoffian, and between the triangular tiling and square tiling, there are seven non-Wythoffian uniform colorings of a total twenty-one that belong to regular tilings (all hexagonal tiling uniform colorings are Wythoffian).
- In two dimensions, there are precisely seven 7-uniform Krotenheerdt tilings, with no other such k-uniform tilings for k > 7, and it is also the only k for which the count of Krotenheerdt tilings agrees with k. In three dimensions, there are collectively 77 Wythoff symbols that represent all uniform polyhedra.
- 7 is the lowest dimension of a known exotic sphere, although there may exist as yet unknown exotic smooth structures on the 4-dimensional sphere.
- When rolling two standard six-sided dice, seven has a 6 in 62 (or 1/6) 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 are seven problems in mathematics that were stated by the Clay Mathematics Institute in 2000. Currently, six of the problems remain unsolved.
|7 × x||7||14||21||28||35||42||49||56||63||70||77||84||91||98||105||112||119||126||133||140||147||154||161||168||175||350||700||7000|
|7 ÷ x||7||3.5||2.3||1.75||1.4||1.16||1||0.875||0.7||0.7||0.63||0.583||0.538461||0.5||0.46|
|x ÷ 7||0.142857||0.285714||0.428571||0.571428||0.714285||0.857142||1.142857||1.285714||1.428571||1.571428||1.714285||1.857142||2||2.142857|
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 = 0.142857 142857... and 2/7 = 0.285714 285714....
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 = 89+5/7; here 5 is the remainder, and would correspond to number 7 in the ranking of the ascending sequence. So in this case, 628 ÷ 7 = 89.714285. Another example, 5238 ÷ 7 = 748+2/7, hence the remainder is 2, and this corresponds to number 2 in the sequence. In this case, 5238 ÷ 7 = 748.285714.
- 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
- 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
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 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
- 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
- Seven days (more precisely yom) of Creation, leading to the seventh day or Sabbath (Genesis 1)
- Seven-fold vengeance visited on upon Cain 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 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 (Proverbs 9:1)
- Seven archangels in the deuterocanonical Book of Tobit (12:15)
References to the number seven in Jewish knowledge and practice include:
- Seven divisions of the weekly readings or aliyah of the Torah
- Seven Jewish men (over the age of 13) called to read aliyahs in Shabbat 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
- Seven loaves multiplied into seven basketfuls of surplus (Matthew 15:32–37)
- Seven demons were driven out of Mary Magdalene (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 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 Seven Sorrows of the Virgin Mary
- Seven Sleepers of Christian myth
- Seven Sacraments in the Catholic Church (though some traditions assign a different number)
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 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)
- Seven Earths and seven Heavens (plural of sky) mentioned in Quran (S. 65:12)
- Seventh day naming ceremony held for babies
- Seven enunciators of divine revelation (nāṭiqs) according to the celebrated Fatimid Ismaili dignitary Nasir Khusraw
- Circle Seven Koran, the holy scripture of the Moorish Science Temple of America
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 "Saptharishi Mandalam" in Indian astronomy
- Seven promises, or Saptapadi, and seven circumambulations around a fire at Hindu weddings
- Seven virgin goddesses or Saptha Kannimar worshipped in temples in Tamil Nadu, India
- Seven hills at Tirumala known as Yedu Kondalavadu in Telugu, or ezhu malaiyan in Tamil, meaning "Sevenhills God"
- Seven steps taken by the Buddha at birth
- Seven divine ancestresses of humankind in Khasi mythology
- Seven octets or Saptak Swaras in Indian Music as the basis for Ragas compositions
- Seven Social Sins listed by Mahatma Gandhi
Other references to the number seven in Eastern traditions include:
- Seven Lucky Gods or gods of good fortune in Japanese mythology
- Seven-Branched Sword in Japanese mythology
- Seven Sages of the Bamboo Grove in China
- Seven minor symbols of yang in Taoist yin-yang
Other references to the number seven in traditions from around the world include:
- Seven palms in an Egyptian 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 and 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 werewolves in Galician folklore, or the son of a woman and a werewolf in other European folklores
- 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 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 Deivės Valdytojos.
- Seven legendary Cities of Gold, such as 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 the Fairies pays a tithe to Hell (or possibly 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
- Seven Dwarfs
- The Seven Brothers, a 1870 novel by Aleksis Kivi
- 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 visual art
- The Group of Seven Canadian landscape painters
- Sports with seven players per side
- 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 extra point is worth seven points.
- Diatonic scale (7 notes)
- Seven colors in the rainbow
- Seven continents
- Seven liberal arts
- Seven Wonders of the Ancient World
- Seven days of the Week
- Septenary (numeral system)
- Year Seven (School)
- Se7en (disambiguation)
- Sevens (disambiguation)
- One-seventh area triangle
- Z with stroke (Ƶ)
- List of highways numbered 7
- Georges Ifrah, The Universal History of Numbers: From Prehistory to the Invention of the Computer transl. David Bellos et al. London: The Harvill Press (1998): 395, Fig. 24.67
- Eeva Törmänen (September 8, 2011). "Aamulehti: Opetushallitus harkitsee numero 7 viivan palauttamista". Tekniikka & Talous (in Finnish). Archived from the original on September 17, 2011. Retrieved September 9, 2011.
- "Education writing numerals in grade 1." Archived 2008-10-02 at the Wayback Machine(Russian)
- "Example of teaching materials for pre-schoolers"(French)
- Elli Harju (August 6, 2015). ""Nenosen seiska" teki paluun: Tiesitkö, mistä poikkiviiva on peräisin?". Iltalehti (in Finnish).
- "Μαθηματικά Α' Δημοτικού" [Mathematics for the First Grade] (PDF) (in Greek). Ministry of Education, Research, and Religions. p. 33. Retrieved May 7, 2018.
- Weisstein, Eric W. "Double Mersenne Number". mathworld.wolfram.com. Retrieved 2020-08-06.
- "Sloane's A088165 : NSW primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-01.
- "Sloane's A050918 : Woodall primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-01.
- "Sloane's A088054 : Factorial primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-01.
- "Sloane's A031157 : Numbers that are both lucky and prime". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-01.
- "Sloane's A035497 : Happy primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-01.
- "Sloane's A003173 : Heegner numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-01.
- Heyden, Anders; Sparr, Gunnar; Nielsen, Mads; Johansen, Peter (2003-08-02). Computer Vision - ECCV 2002: 7th European Conference on Computer Vision, Copenhagen, Denmark, May 28-31, 2002. Proceedings. Part II. Springer. p. 661. ISBN 978-3-540-47967-3.
A frieze pattern can be classified into one of the 7 frieze groups...
- Weisstein, Eric W. "Heptagon". mathworld.wolfram.com. Retrieved 2020-08-25.
- Weisstein, Eric W. "7". mathworld.wolfram.com. Retrieved 2020-08-07.
- Sloane, N. J. A. (ed.). "Sequence A000566 (Heptagonal numbers (or 7-gonal numbers))". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2023-01-09.
- Sloane, N. J. A. (ed.). "Sequence A003215". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-01.
- Grünbaum, Branko; Shepard, Geoffrey (November 1977). "Tilings by Regular Polygons" (PDF). Mathematics Magazine. Taylor & Francis, Ltd. 50 (5): 231. doi:10.2307/2689529. JSTOR 2689529. S2CID 123776612. Zbl 0385.51006.
- Jardine, Kevin. "Shield - a 3.7.42 tiling". Imperfect Congruence. Retrieved 2023-01-09. 3.7.42 as a unit facet in an irregular tiling.
- Grünbaum, Branko; Shepard, Geoffrey (November 1977). "Tilings by Regular Polygons" (PDF). Mathematics Magazine. Taylor & Francis, Ltd. 50 (5): 229-230. doi:10.2307/2689529. JSTOR 2689529. S2CID 123776612. Zbl 0385.51006.
- Coxeter, H. S. M. (1999). "Chapter 3: Wythoff's Construction for Uniform Polytopes". The Beauty of Geometry: Twelve Essays. Mineola, NY: Dover Publications. pp. 326–339. ISBN 9780486409191. OCLC 41565220. S2CID 227201939. Zbl 0941.51001.
- Grünbaum, Branko; Shephard, G. C. (1987). "Section 2.1: Regular and uniform tilings". Tilings and Patterns. New York: W. H. Freeman and Company. pp. 62–64. ISBN 0-7167-1193-1. OCLC 13092426. S2CID 119730123.
- Grünbaum, Branko; Shephard, G. C. (1987). "Section 2.9 Archimedean and uniform colorings". Tilings and Patterns. New York: W. H. Freeman and Company. pp. 102–107. ISBN 0-7167-1193-1. OCLC 13092426. S2CID 119730123.
- Sloane, N. J. A. (ed.). "Sequence A068600 (Number of n-uniform tilings having n different arrangements of polygons about their vertices.)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2023-01-09.
- Grünbaum, Branko; Shepard, Geoffrey (November 1977). "Tilings by Regular Polygons" (PDF). Mathematics Magazine. Taylor & Francis, Ltd. 50 (5): 236. doi:10.2307/2689529. JSTOR 2689529. S2CID 123776612. Zbl 0385.51006.
- Messer, Peter W. (2002). "Closed-Form Expressions for Uniform Polyhedra and Their Duals" (PDF). Discrete & Computational Geometry. Springer. 27: 353–355, 372–373. doi:10.1007/s00454-001-0078-2. MR 1921559. S2CID 206996937. Zbl 1003.52006.
- Antoni, F. de; Lauro, N.; Rizzi, A. (2012-12-06). COMPSTAT: Proceedings in Computational Statistics, 7th Symposium held in Rome 1986. Springer Science & Business Media. p. 13. ISBN 978-3-642-46890-2.
...every catastrophe can be composed from the set of so called elementary catastrophes, which are of seven fundamental types.
- Weisstein, Eric W. "Dice". mathworld.wolfram.com. Retrieved 2020-08-25.
- "Millennium Problems | Clay Mathematics Institute". www.claymath.org. Retrieved 2020-08-25.
- "Poincaré Conjecture | Clay Mathematics Institute". 2013-12-15. Archived from the original on 2013-12-15. Retrieved 2020-08-25.
- Bryan Bunch, The Kingdom of Infinite Number. New York: W. H. Freeman & Company (2000): 82
- Gonzalez, Robbie (4 December 2014). "Why Do People Love The Number Seven?". Gizmodo. Retrieved 20 February 2022.
- Bellos, Alex. "The World's Most Popular Numbers [Excerpt]". Scientific American. Retrieved 20 February 2022.
- Kubovy, Michael; Psotka, Joseph (May 1976). "The predominance of seven and the apparent spontaneity of numerical choices". Journal of Experimental Psychology: Human Perception and Performance. 2 (2): 291–294. doi:10.1037/0096-15126.96.36.1991. Retrieved 20 February 2022.
- "Number symbolism - 7".
- "Nāṣir-i Khusraw", An Anthology of Philosophy in Persia, I.B.Tauris, 2001, doi:10.5040/9780755610068.ch-008, ISBN 978-1-84511-542-5, retrieved 2020-11-17
- Rajarajan, R.K.K. (2020). "Peerless Manifestations of Devī". Carcow Indological Studies (Cracow, Poland). XXII.1: 221–243. doi:10.12797/CIS.22.2020.01.09. S2CID 226326183.
- Rajarajan, R.K.K. (2020). "Sempiternal "Pattiṉi": Archaic Goddess of the vēṅkai-tree to Avant-garde Acaṉāmpikai". Studia Orientalia Electronica (Helsinki, Finland). 8 (1): 120–144. doi:10.23993/store.84803. S2CID 226373749.
- "Encyclopædia Britannica "Number Symbolism"". Britannica.com. Retrieved 2012-09-07.
- Klimka, Libertas (2012-03-01). "Senosios baltų mitologijos ir religijos likimas". Lituanistica. 58 (1). doi:10.6001/lituanistica.v58i1.2293. ISSN 0235-716X.
- "Chapter I. The Creative Thesis of Perfection by William S. Sadler, Jr. - Urantia Book - Urantia Foundation". urantia.org. 17 August 2011.
- Yemaya. Santeria Church of the Orishas. Retrieved 25 November 2022
- Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group (1987): 70–71