Normal order for divisor functions of generalized integers Horadam, E.M. — 1968 Portugaliae mathematica
Ramanujan's Sum and Nagell's Totient Functio for Arithmetical Semi-Groups. E.M. Horadam — 1968 Mathematica Scandinavica
An extension of Daykin's generalized Möbius function to unitary divisors. E.M. Horadam — 1971 Journal für die reine und angewandte Mathematik
The average order of the number of generalised integers representable as a product of a prime and a square. E.M. Horadam — 1965 Journal für die reine und angewandte Mathematik
Exponential functions for arithmetical semi-groups. E.M. Horadam — 1966 Journal für die reine und angewandte Mathematik