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Dirichlet series

A general Dirichlet series is a series of the form ∑ n = 1 ∞ a n e − λ n s. {\textstyle \sum _{n=1}^{\infty }a_{n}e^{-\lambda _{n}s}.} One important special case of this is the ordinary Dirichlet series ∑ n = 1 ∞ a n n s. {\textstyle \sum _{n=1}^{\infty }{\frac {a_{n}}{n^{s}}}.} Used in number theory.