Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
@ Max Alekseyev: But you then get $a_{n}= 2(n+1)(2n+1)^{3} $ and $b_{n }= -(n-1)(n+1)(2n+1)^{3}$ and there is no possibility of division unless $n$ is odd.