Here's the question you clicked on:
koli123able
What is the nth term of: 1^2 + (1^2+2^2) + (1^2+2^2+3^2)+.....
\[an = \frac{ n(n+1)(2n+1) }{ 6 }\]
Do you see how the nth term is something like \[1^2+2^2+\cdots+(n-1)^2+n^2?\] What's the sum of all square numbers from 1 to n? i.e., \[\sum_{k=1}^n k^2?\]