# Dirichlet series

In

mathematics, a

**Dirichlet series**, one of a number of concepts named in honor of

Johann Peter Gustav Lejeune Dirichlet, is a

series of the form

The most famous of Dirichlet series is

which is the

Riemann zeta function.

Other Dirichlet series are:

where μ(

*n*) is the Möbius function,

where φ(

*n*) is the

totient function, and

where σ

_{a}(

*n*) is the

divisor function.