KOLBERG, O. Über ein Problem von Viggo Brun. Mathematica Scandinavica, Berkeley, CA, United States, v. 3, p. 221–223, 1955. DOI: 10.7146/math.scand.a-10439. Disponível em: https://journals.msp.org/mscand/article/view/2887. Acesso em: 8 sep. 2026.