a(n) is the concatenation in increasing order of all single-digit divisors of n.

Terms

a(0) =1a(1) =12a(2) =13a(3) =124a(4) =15a(5) =1236a(6) =17a(7) =1248a(8) =139a(9) =125a(10) =1a(11) =12346a(12) =1a(13) =127a(14) =135a(15) =1248a(16) =1a(17) =12369a(18) =1a(19) =1245a(20) =137a(21) =12a(22) =1a(23) =123468a(24) =15a(25) =12a(26) =139a(27) =1247a(28) =1a(29) =12356