Positive integers read backwards, but omit a number if it is <= an earlier number.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =6a(6) =7a(7) =8a(8) =9a(9) =11a(10) =21a(11) =31a(12) =41a(13) =51a(14) =61a(15) =71a(16) =81a(17) =91a(18) =92a(19) =93a(20) =94a(21) =95a(22) =96a(23) =97a(24) =98a(25) =99a(26) =101a(27) =201a(28) =301a(29) =401