eighteenth letter of the Greek alphabet

Sigma (uppercase/lowercase Σ σ ς) is the 18th letter of the Greek alphabet. It is used to represent the "s" sound in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 200. Letters that came from it include the Roman S and Cyrillic С.



The uppercase Σ is the shorthand symbol for summation (the symbol is also known as the summation operator).[1] It is often used to condense Taylor series and to write out trigonometric functions such as sine, cosine, and tangent as series.

The lowercase σ is used to represent population standard deviation in statistics, and permutation function in abstract algebra.[1][2]



  1. 1.0 1.1 "Greek/Hebrew/Latin-based Symbols in Mathematics". Math Vault. 2020-03-20. Retrieved 2020-10-07.
  2. "Sigma Symbol in Greek Alphabet". Retrieved 2020-10-07.