OJALA, T. Sums of roots of unity. MATHEMATICA SCANDINAVICA, [S. l.], v. 37, p. 83–101, 1975. DOI: 10.7146/math.scand.a-11590. Disponível em: https://www.mscand.dk/article/view/11590. Acesso em: 4 may. 2024.