3 (N + 1)3 - 2 (N + 1)2 + 6 N + 6 > SUM(K^2, K=1....

1/3 (n + 1)

3

- 1/2 (n + 1)

2

+ 1/6 n + 1/6 > sum(1/k^2, k=1..infinity);