The ∫ symbol 
is used to denote the integral in mathematics. The notation was introduced by the German mathematician Gottfried Wilhelm von Leibniz towards the end of the 17th century. The symbol was based on the ſ (long s) character, and was chosen because the integral is a limit of sums. See long s for more details on the history of ſ.
The ∫ symbol is U+222B in Unicode and \int in LaTeX. In HTML, it is written as ∫ (hexadecimal), ∫ (decimal) and ∫ (named entity).
The original IBM PC code page 437 character set included a couple of characters ⌠ and ⌡ (codes 244 and 245, respectively) to build the integral symbol. These were deprecated in subsequent MS-DOS code pages, but they still remain in Unicode (U+2320 and U+2321, respectively) for compatibility.
The ∫ symbol is very similar to, but not to be confused with, the (ʃ) symbol (called esh).
Related symbols are ∬ (double integral, U+222C), ∭ (triple integral, U+222D), ∮ (contour integral, U+222E), ∯ (surface integral, U+222F), and ∰ (volume integral, U+2230).
Typography in other languages
In other languages, the shape of the integral symbol differs slightly from the shape commonly seen in English-language textbooks.
 In English-language mathematical literature, the stem of the integral symbol leans to the right |
 The German integral symbol has a vertical stem |
 The Russian integral symbol has a left-leaning stem (German-style integrals are also sometimes seen in Russian literature) |
Another difference is in the placement of limits for definite integrals. In English-language books, limits go to the right of the integral symbol: 
By contrast, in German and Russian tradition, limits go above and below the integral symbol, making the mathematical formula take up more vertical space: 
References
- Stewart, James (2003). "Integrals". Single Variable Calculus: Early Transcendentals (5th edition ed.). Belmont, CA: Brooks/Cole. p. 381. ISBN 0-534-39330-6.
- Zaitcev, V.; Janishewsky, A.; Berdnikov, A. (1999), "Russian Typographical Traditions in Mathematical Literature", EuroTeX'99 Proceedings
External links
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