双线 N 元求和 ⅀

「Double-Struck N-Ary Summation」 is a letter belonging to the modern Greek alphabet. It represents the sound ] in writing. It was that very letter which the Latin S and the Cyrillic С originated from. The uppercase letter is used as a symbol of summation in mathematics. As for physics, there it denotes a special type of elementary particles called hyperons. The numerical value of sigma is 200.

Unicode offers various sigma versions, including the doubly outlined sign of N-Ary Summation, which you can copy from this page. For most general purposes, the standard uppercase sigma Σ is likely the most suitable, as it's widely used in mathematics and physics.

符号 「双线 N 元求和」 包含在 「字母式符号」 块的 「雙重打擊大型操作員」 子块中，并在2002年作为Unicode版本3.2的一部分获得批准。