WILLIAMS, Kenneth S. 3 as a Ninth Power (mod $p$). Mathematica Scandinavica, Berkeley, CA, United States, v. 35, p. 309–317, 1974. DOI: 10.7146/math.scand.a-11555. Disponível em: https://journals.msp.org/mscand/article/view/2093. Acesso em: 25 jul. 2026.