Σ

 Σ U+03A3, Σ GREEK CAPITAL LETTER SIGMA
 [unassigned: U+03A2]

Translingual

Symbol

Σ

1. (mathematics) Σ. Sum over a set of like terms:
${\displaystyle \sum _{n=1}^{2}n^{2}=1^{2}+2^{2}=5}$
2. (topology) suspension or reduced suspension
3. (mathematics) A class (in the arithmetical hierarchy) of formulae whose outermost unbounded quantifiers are existential quantifiers

Usage notes

(mathematics): Though there exists a distinct symbol () for the purpose of the mathematical summation, the upper case sigma here is often used for convenience.

Coordinate terms

• (classification of formulae): Π, Δ

Greek

Letter

Σ ‎(S) ‎(uppercase, lowercase σ)

1. The upper case letter sigma (σίγμα), the 18th letter of the modern Greek alphabet.