I have this sequence :
 4,12,24,48,240,720,....

I order to find nth term of this sequence , can we represent this sequence as a function of n.


Question: The Riemann Integrability of a function similar to Dirichlet's function
Answer: A nice theorem to know is that a bounded function is Riemann integrable if and only if the set of its discontinuities has measure zero.  Your function is only continuous at 0.  So since your interval is uncountable, $f$ is NOT Riemann Integrable.