TITLE: Find $\sum\limits_{k=1}^n \frac{1}{k}\binom{n}{k}$
QUESTION [7 upvotes]: I would like to find $\sum\limits_{k=1}^n \frac{1}{k}\binom{n}{k}$.
I tried to write this as an integral but I can't find the result.

REPLY [4 votes]: Let $$f(x)=\sum_{k=1}^n\frac1k{n\choose k}x^k$$
We are interested in $f(1)$ and note that
$$ f'(x)=\sum_{k=1}^n{n\choose k}x^{k-1}=\frac1x\sum_{k=1}^n{n\choose k}x^{k}=\frac{(1+x)^n-1}{x}$$
so that
$$f(1)=f(0)+\int_0^1f'(x)\,\mathrm dx=\int_0^1 \frac{(1+x)^n-1}{x}\,\mathrm dx$$