HJELLE, T.; KLOVE, T. Congruence Properties and Density Problems for the Fourier Coefficients of Modular Forms. Mathematica Scandinavica, Berkeley, CA, United States, v. 23, p. 160–166, 1968. DOI: 10.7146/math.scand.a-10905. Disponível em: https://journals.msp.org/mscand/article/view/2442. Acesso em: 25 jul. 2026.