In the beginning, various Hindus wrote 7 more or less in one stroke as a curve that looks like an uppercaseJ 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 character more rectilinear. The eastern Arabs developed the character from a 6 lookalike into an uppercase V lookalike. 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, 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 1. In some Greek dialects of 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 number with the most common glyph variation. 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 as ① in the illustration to the right. While the shape of the 7 character 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, sometimes with the top line crooked. The line through the middle is useful to clearly differentiate the character from the number one, as the two can appear similar when written in certain styles of handwriting. This glyph 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.
Seven is the lowest natural number that cannot be represented as the sum of the squares of three integers.
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 lowest dimension of a known exotic sphere, 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 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, and
