LANKE, Jan. On the Asymptotic Distribution of Eigenvalues of Certain One-Dimensional Sturm-Liouville Operators. Mathematica Scandinavica, Berkeley, CA, United States, v. 9, p. 69–79, 1961. DOI: 10.7146/math.scand.a-10623. Disponível em: https://journals.msp.org/mscand/article/view/2722. Acesso em: 25 jul. 2026.