AL-SALAM, W. A. On the product of two Legendre polynomials. MATHEMATICA SCANDINAVICA, [S. l.], v. 4, p. 239–242, 1956. DOI: 10.7146/math.scand.a-10471. Disponível em: https://www.mscand.dk/article/view/10471. Acesso em: 11 apr. 2025.