N-Ary Summation

It means add the specified terms across the given range. The index and starting value appear below ∑, the stopping value sits above, and the formula to add follows to the right. Leonhard Euler introduced Greek capital sigma for sums in 1755, often remembered as matching the initial of sum; the notation spread gradually through nineteenth-century mathematics.

In plain text, ∑ remains standard text height. In a displayed equation, a math typesetter makes ∑ larger and puts the limits directly above and below it, while inline text keeps them to the right.