Previous work has shown how Laplace Transform Theory and z-Transform Theory may be. used in Net Present Value Analysis. A closed-form expression is easily derived for a continuouscash flow tk, where t denotes time and k is a positive integer. In the corresponding discrete case, explicit expressions have only been provided for k < 10. In this article we derive a closed-form formula for the missing general case when k is an arbitrary non-negative integer. As a byproduct, we also obtain a closed-form expression for the z-transform of such a power series.