$\sum_{i=0}^{n} \sum_{j=0}^{i-1} (i+1)$
Not totally sure how to get passed this one. I brought it down from a triple to a double, but I'm having trouble with the fact that $i$ is the what is being added.
My thought is that it will be $\sum_{i=0}^{n} (i+1)^2$ but I cant say that with total certainty.
Thanks for the help.