The eighteenth Greek letter. In Greek, if the last letter of a word is lowercase sigma, what should it be written as? This letter is also called final sigma(Unicode: U+03C2). In modern Greece, this number stands for 6. In mathematics, we use it as a summation symbol.

Capital σ is used for mathematical summation symbols, such as ∑Pi, where i= 1, 2, ..., t, which is the sum of P 1+P2+ and ...+angle. Lowercase σ is used for statistical standard deviation. Both the с of Cyrillic alphabet and the S of Latin alphabet are derived from Sigma.

It also means summation, which means ∑ j =1+2+3+…+n.

Where I stands for the lower bound, n stands for the upper bound, and k starts from I and goes all the way to n, all of which add up.

∑ i can also be expressed as the sum of I, which is a variable.