What is the finite sum of an alternating odd sequence with binomial coefficients: $ \ \sum_{k=0}^{j} \binom{j}{k} \ \frac{(-1)^k}{2k+1}$?
Proving a binomial sum identity $\sum _{k=0}^n \binom nk \frac{(-1)^k}{2k+1} = \frac{(2n)!!}{(2n+1)!!}$