ASKEY, Richard; HIRSCHMAN, I. I. Jr. Mean Summability for Ultraspherical Polynomials. Mathematica Scandinavica, Berkeley, CA, United States, v. 12, p. 167–177, 1963. DOI: 10.7146/math.scand.a-10680. Disponível em: https://journals.msp.org/mscand/article/view/2648. Acesso em: 25 jul. 2026.