Σ Sigma Symbol (Uppercase / Summation)

Uppercase sigma (Σ) denotes summation; the dedicated math summation sign is ∑ (U+2211), which looks nearly identical.

Also known as: summation symbol, sum symbol, greek capital letter sigma, ∑.

Codes

WindowsAlt + 228

Alt + 228 gives the Greek letter Σ. For the summation sign ∑, use Alt + 8721 or type 2211 then Alt + X in Word.

Mac

Open Character Viewer (Control + Cmd + Space), search “greek capital letter sigma” (Σ) or “n-ary summation” (∑), and double-click it.

Microsoft Word03A3, Alt + X

Type 03A3 then Alt + X for Σ (use 2211 then Alt + X for ∑).

Google Docs

Insert → Special characters, then search “sigma” (Σ) or “summation” (∑).

LaTeX\sum

Use \sum for the large summation operator with limits, or \Sigma for the plain Greek letter.

Σ denotes summation: Σ from i=1 to n of aᵢ adds the terms a₁ + a₂ + … + aₙ.
The dedicated math summation sign is ∑ (U+2211); the Greek capital letter is Σ (U+03A3) — nearly identical in appearance.
In LaTeX, \sum renders the large operator with limits; \Sigma is just the letter.