ERDÖS, P. On the Integers Relatively Prime to $n$ and a Number-Theoretic Function Considered by Jacobsthal. Mathematica Scandinavica, Berkeley, CA, United States, v. 10, p. 163–170, 1962. DOI: 10.7146/math.scand.a-10523. Disponível em: https://journals.msp.org/mscand/article/view/2667. Acesso em: 25 jul. 2026.