https://math.stackexchange.com/questions/48080/sum-of-first-n-squares-equals-fracnn12n16 https://math.stackexchange.com/questions/1802846/how-can-you-prove-that-1-5-9-cdots-4n-3-2n2-n-without-using-ind/1803901#1803901 http://www.math.pitt.edu/~sparling/23021/23021sums2/node5.html