Question 892532
That's the Greek letter sigma, btw. For example:


*[tex \large \sum_{n=0}^k n^2 = \frac{k(k+1)(2k+1)}{6}]


If k = 3, then *[tex \large \sum_{n=0}^3 n^2 = 0^3 + 1^2 + 2^2 + 3^2 = 14 = \frac{3(4)(7)}{6}] which is a true statement.


Basically, just replace the index (in the above case, n) with its starting value and increment until you get to the top number, and add everything up.