SELMER, Ernst S. On the postage stamp problem with three stamp denominations, III. Mathematica Scandinavica, Berkeley, CA, United States, v. 56, p. 105–116, 1985. DOI: 10.7146/math.scand.a-12091. Disponível em: https://journals.msp.org/mscand/article/view/1536. Acesso em: 25 jul. 2026.