sentences:  This is used in the definition of Dirichlet density.This gives the continuation of "P"("s") to formula_6, with an infinite number of logarithmic singularities at points "s" where "ns" is a pole (only "ns" = 1 when "n" is a squarefree number greater than or equal to 1), or zero of the Riemann zeta function "ζ"(.