SELMER, Ernst S. On the postage stamp problem with three stamp denominations, III. MATHEMATICA SCANDINAVICA, [S. l.], v. 56, p. 105–116, 1985. DOI: 10.7146/math.scand.a-12091. Disponível em: https://tidsskrift.dk/math/article/view/12091. Acesso em: 13 aug. 2026.