Numbers whose base-10 representation has the same nonzero number of 4's and 5's.

Terms

a(0) =45a(1) =54a(2) =145a(3) =154a(4) =245a(5) =254a(6) =345a(7) =354a(8) =405a(9) =415a(10) =425a(11) =435a(12) =450a(13) =451a(14) =452a(15) =453a(16) =456a(17) =457a(18) =458a(19) =459a(20) =465a(21) =475a(22) =485a(23) =495a(24) =504a(25) =514a(26) =524a(27) =534a(28) =540a(29) =541