rearranging the given expression,
C0-C0/2+C1-C1/3....
which is (C0+C1+C2....)-(C0/2+C1/3+C2/4...)
the first bracket series upto n terms is 2n and the second bracket sum can also be found out by writing the binomial expansion of x(1+x)n,integrating it and putting x=1.