Morris Marden, Logarithmic Derivative of an Entire Function, Proceedings of the American Mathematical Society, Vol. 28, No. 2 (May, 1971), pp. 513-518 ...

The Riemann hypothesis is equivalent to the Li criterion governing a sequence of real constants $\{\lambda _{k}\}_{k=1}^{\infty}$ that are certain logarithmic derivatives of the Riemann xi function ...