1-digit numbers in reverse alphabetical order, then 2-digit numbers, etc.

Terms

a(0) =0a(1) =2a(2) =3a(3) =6a(4) =7a(5) =1a(6) =9a(7) =4a(8) =5a(9) =8a(10) =22a(11) =23a(12) =26a(13) =27a(14) =21a(15) =29a(16) =24a(17) =25a(18) =28a(19) =20a(20) =12a(21) =32a(22) =33a(23) =36a(24) =37a(25) =31a(26) =39a(27) =34a(28) =35a(29) =38