SELMER, Ernst S.; RÖDNE, Arne. On the postage stamp problem with three stamp denominations, II. Mathematica Scandinavica, Berkeley, CA, United States, v. 53, p. 145–156, 1983. DOI: 10.7146/math.scand.a-12022. Disponível em: https://journals.msp.org/mscand/article/view/1650. Acesso em: 25 jul. 2026.