Notations. As usual, Z is the ring of rational integers, Z >0 the set of positive integers, C the field of complex numbers. We denote by h the upper half-plane, and by Γ the full modular group PSL 2 (Z). For a complex variable s, we put e(s) = e 2πis , Γ R (s) = π −s/2 Γ (s/2) and Γ C (s) = 2(2π) −s Γ (s). We denote by ζ(s) and ζ * (s) = Γ R (s)ζ(s) the Riemann zeta-function and the completed Riemann zeta-function, respectively, and denote by σ ν (n) = d|n d ν the divisor function. Throughout the paper, z = x + iy (x ∈ R, y > 0) is a variable on h, and s = σ + it (σ, t ∈ R) is a complex variable. A sum over the empty set is meant to be zero.