Numbers that have only the straight digits {1, 4, 7}.

Terms

a(0) =1a(1) =4a(2) =7a(3) =11a(4) =14a(5) =17a(6) =41a(7) =44a(8) =47a(9) =71a(10) =74a(11) =77a(12) =111a(13) =114a(14) =117a(15) =141a(16) =144a(17) =147a(18) =171a(19) =174a(20) =177a(21) =411a(22) =414a(23) =417a(24) =441a(25) =444a(26) =447a(27) =471a(28) =474a(29) =477