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Playing with additivity conditions in multiplicative functions

Crystel Bujold and Isabelle Taylor-Daoust

Vol. 15 (2026), No. 3, 217–226
Abstract

Let f : ℤ → ℂ be a multiplicative function. Assume there exist integers a > 1 and d > 1 such that (a,d) = 1, and let 𝒫a,d = {a + kd : k ∈ ℤ}. Under mild extra conditions on d and f(a), we prove that f(n) = nχ(n) for all n outside an explicit exceptional set depending on d, and some Dirichlet character χ.

Keywords
multiplicative functions, additivity, arithmetic progressions, Dirichlet characters
Mathematical Subject Classification
Primary: 11A99, 11B25, 11N99, 11A25
Milestones
Received: 16 July 2025
Revised: 22 June 2026
Accepted: 24 July 2026
Published: 16 October 2026
Authors
Crystel Bujold
Mathématiques
Collège Bois-de-Boulogne
Montreal, QC
Canada
Isabelle Taylor-Daoust
Mathématiques
Collège Bois-de-Boulogne
Montreal, QC
Canada