Values increase, Roman numerals increase lexicographically.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =6a(6) =7a(7) =8a(8) =10a(9) =11a(10) =12a(11) =13a(12) =14a(13) =15a(14) =16a(15) =17a(16) =18a(17) =20a(18) =21a(19) =22a(20) =23a(21) =24a(22) =25a(23) =26a(24) =27a(25) =28a(26) =30a(27) =31a(28) =32a(29) =33