Integral Symbol
The ∫ symbol is used to denote the integral in mathematics. The notation was introduced by the German mathematician Gottfried Wilhelm Leibniz towards the end of the 17th century. The symbol was based on the ſ (long s) character, and was chosen because Leibniz thought of the integral as an infinite sum of infinitesimal summands. 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), ∯ (closed surface integral, U+222F), and ∰ (closed volume integral, U+2230).
Read more about Integral Symbol: Typography in Other Languages
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