SELMER, E. S. On the postage stamp problem with the three stamp denominations. MATHEMATICA SCANDINAVICA, [S. l.], v. 47, p. 29–71, 1980. DOI: 10.7146/math.scand.a-11874. Disponível em: https://www.mscand.dk/article/view/11874. Acesso em: 3 may. 2024.