Apply ∑i=n(n+1)2\sum i = \frac{n(n+1)}{2}∑i=2n(n+1), ∑i2=n(n+1)(2n+1)6\sum i^2 = \frac{n(n+1)(2n+1)}{6}∑i2=6n(n+1)(2n+1), etc.
