RAJAGOPAL, C. T. On an absolute constant for a class of power series. Mathematica Scandinavica, Berkeley, CA, United States, v. 5, p. 267–270, 1957. DOI: 10.7146/math.scand.a-10504. Disponível em: https://journals.msp.org/mscand/article/view/2820. Acesso em: 25 jul. 2026.