# Σ

 Σ U+03A3, Σ GREEK CAPITAL LETTER SIGMA
 [unassigned: U+03A2]
 ← Ρ[U+03A1] Greek and Coptic Τ →[U+03A4]

## Translingual

### Symbol

Σ

1. Σ. Sum over a set of like terms:
${\displaystyle \sum _{n=1}^{3}n^{2}=1^{2}+2^{2}+3^{2}=14}$
2. (topology) suspension or reduced suspension
3. 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

## Ancient Greek

### Etymology

From Phoenician𐤔(š, šīn).

### Letter

Σ (S) (uppercase, nonfinal lowercase σ, final lowercase ς)

1. The letter sigma (σίγμα), the 18th letter of the ancient Greek alphabet.

## Greek

### Letter

Σ (S) (uppercase, lowercase σ)

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

### Numeral

Σ (S)

1. The number 200 in Greek numerals.

1. The number 200,000 in Greek numerals.