|Roman numeral||VII, vii|
|Greek numeral||Z, ζ|
|Arabic, Kurdish, Persian||٧|
|Chinese numeral||七, 柒|
7 (seven) is the natural number following 6 and preceding 8. It is the only prime number preceding a cube.
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.
In the beginning, Indians wrote 7 more or less in one stroke as a curve that looks like an uppercase ⟨J⟩ vertically inverted (ᒉ). 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 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.
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, 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.
|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.
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:
Main article: Significance of numbers in Judaism
The number seven forms a widespread typological pattern within Hebrew scripture, including:
References to the number seven in Jewish knowledge and practice include:
Following the traditional of the Hebrew Bible, the New Testament likewise uses the number seven as part of a typological pattern:
References to the number seven in Christian knowledge and practice include:
References to the number seven in Islamic knowledge and practice include:
References to the number seven in Hindu knowledge and practice include:
Other references to the number seven in Eastern traditions include:
Other references to the number seven in traditions from around the world include:
A frieze pattern can be classified into one of the 7 frieze groups...
...every catastrophe can be composed from the set of so called elementary catastrophes, which are of seven fundamental types.