Prove for the Bernoulli numbers $B_n$, that for all $a \in \mathbb{N}$, that $ \sum_{i=0}^{2a+1} {2a+1 \choose i} B_{2a+1-i} [ (n+1)^i+(-n)^i ] =0 $. As much as this is a neat identity, it's a crucial step in another result concerning powersums. I have no idea how to prove it, aside from noting that it cannot be directly evaluated by powersums. Any ideas for a proof?