KATRE, S. A.; RAJWADE, A. R. On the Jacobsthal sum $\phi_9(a)$ and the related sum $\psi_9(a)$. Mathematica Scandinavica, Berkeley, CA, United States, v. 53, p. 193–202, 1983. DOI: 10.7146/math.scand.a-12026. Disponível em: https://journals.msp.org/mscand/article/view/1642. Acesso em: 25 jul. 2026.