Thursday, July 21, 2016

sequences and series - How to prove sumlimitsNk=0frac(1)kNchoosek(k+1)2=frac1N+1sumlimitsN+1n=1frac1n

In the process of proving a more complicated relation, I've come across the following equality that I'm having trouble proving:



\sum\limits_{k=0}^{N} \frac{(-1)^k {N \choose k}}{(k+1)^2} = \frac{1}{N+1} \sum\limits_{n=1}^{N+1} \frac{1}{n}



I was already able to prove the following similar equality:



\sum\limits_{k=0}^N \frac{(-1)^k {N \choose k}}{k+1} = \frac{1}{N + 1}



but I'm unsure how to proceed with the first one. I assume it has something to do with the fact that every term in the left hand side of the first equality is \frac{1}{k+1} times a term in the left hand side of the second equality. Any help would be greatly appreciated.

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