⅀

Character	⅀
Unicode name	DOUBLE-STRUCK N-ARY SUMMATION
Unicode block	Letterlike Symbols
Codepoint	U+2140
ℿ ← Letterlike Symbols → ⅁

See also: ∑ [U+2211 N-ARY SUMMATION] and Σ [U+03A3 GREEK CAPITAL LETTER SIGMA]

Translingual

Symbol

⅀

1. (mathematics) A double-struck n-ary summation operator, resembling a Greek capital letter sigma