1/n^(1/2+it) is analytic at z=1/2+it So by cauchys integral theorem Integral 1/n^(1/2+it)dz=0 Taking derivative we get d/dz integral 1/n^(1/2+it)dz=0 d integral 1/n^(1/2+it)=0 1/n^(1/2+it)=0 So is it correct i think its wrong.