+0

0
133
1

The closed form sum of $$12 \left[ 1^2 \cdot 2 + 2^2 \cdot 3 + \ldots + n^2 (n+1) \right]$$

for $n \geq 1$  is $n(n+1)(n+2)(an+b).$  Find $an + b.$

Mar 16, 2021