I am computing the time-complexity of an algorithm and came up with the following summation. I plugged it in to Wolfram Alpha to see what the result is. Unfortunately, WA does not show the steps of this particular solution. Can someone show me how it got the right side of the equation?
$\sum_{i=1}^n i(n-i) = \frac{1}{6} (n - 1) n (n + 1)$
