ERDÖS, P. On the Integers Relatively Prime to $n$ and a Number-Theoretic Function Considered by Jacobsthal. MATHEMATICA SCANDINAVICA, [S. l.], v. 10, p. 163–170, 1962. DOI: 10.7146/math.scand.a-10523. Disponível em: https://www.mscand.dk/article/view/10523. Acesso em: 5 may. 2024.