DIRDAL, Gunnar. Congruence properties for a class of arithmetical functions. MATHEMATICA SCANDINAVICA, [S. l.], v. 38, p. 247–261, 1976. DOI: 10.7146/math.scand.a-11632. Disponível em: https://tidsskrift.dk/math/article/view/11632. Acesso em: 14 aug. 2026.