The sum of n terms of the series whose nth term is n(n+1) is equal to
Tπ = n2 + n ⇒ Sπ = ∑Tπ = ∑ n2 + ∑n
= n(n+1)(2n+1)6 + n(n+1)2
= n(n+1)6 {2n + 1 + 3} = n(n+1)(n+2)3