a(0)=0; a(1)=2. Slowest increasing sequence where every digit "d" has a copy of itself in a(n+d).

Terms

a(0) =0a(1) =2a(2) =3a(3) =12a(4) =13a(5) =123a(6) =124a(7) =132a(8) =213a(9) =214a(10) =1234a(11) =1235a(12) =1236a(13) =1243a(14) =1324a(15) =1325a(16) =1352a(17) =1423a(18) =12346a(19) =12347a(20) =12350a(21) =12354a(22) =12364a(23) =12374a(24) =12376a(25) =12435a(26) =123457a(27) =123458a(28) =123459a(29) =123460