I've this problem, maybe I should use M-weierstrass test, but I really don't know. I appreciate your help.

I must find the domain of the function, the biggest set where the function is continuous and the biggest set where the function is differentiable.

$\displaystyle f(x) = \displaystyle \sum_{n=0}^\infty \frac{e^{-nx}}{n^2+1}$

Thanks

everk