Logarithmic derivative
= Logarithmic derivative
{wiki}
The logarithmic derivative of a nonzero differentiable function $f$ is $f'/f$. For $\Re s>1$, the <Euler product> for the <Riemann zeta function> gives
$$
-\frac{\zeta'(s)}{\zeta(s)}
=\sum_{n\geq1}\frac{\Lambda(n)}{n^s}.
$$