ASKEY, Richard; HIRSCHMAN, I. I. Jr. Mean Summability for Ultraspherical Polynomials. MATHEMATICA SCANDINAVICA, [S. l.], v. 12, p. 167–177, 1963. DOI: 10.7146/math.scand.a-10680. Disponível em: https://www.mscand.dk/article/view/10680. Acesso em: 5 dec. 2025.