\prod_{k=2}^n \frac{(k-1)(k^2+k+1)}{(k+1)(k^2-k+1)}=\prod_{k=2}^n \frac{(k-1)}{(k+1)}\cdot\prod_{k=2}^n \frac{(k^2+k+1)}{(k^2-k+1)}