Numbers whose set of base-10 digits is {1,4}.

Terms

a(0) =1a(1) =4a(2) =11a(3) =14a(4) =41a(5) =44a(6) =111a(7) =114a(8) =141a(9) =144a(10) =411a(11) =414a(12) =441a(13) =444a(14) =1111a(15) =1114a(16) =1141a(17) =1144a(18) =1411a(19) =1414a(20) =1441a(21) =1444a(22) =4111a(23) =4114a(24) =4141a(25) =4144a(26) =4411a(27) =4414a(28) =4441a(29) =4444