Does the Riemann integral of the following function equal $0$?
$ f(x) = \left\{ \begin{array}{ll} 1 , & \hbox{if } x=\frac{1}{n};\\ 0 , & \hbox{otherwsie.} \end{array} \right. $
I need to prove it is integrable; now I can do that with Darboux. But I also tried with Riemann sums and got that the integral is $0$ in the interval $(0,1)$. but I am not so sure I was doing it right...