Numbers k such that 1 and 3 occur juxtaposed in the base-10 representation of k but not of k-1.

Terms

a(0) =13a(1) =31a(2) =113a(3) =130a(4) =213a(5) =231a(6) =310a(7) =331a(8) =413a(9) =431a(10) =513a(11) =531a(12) =613a(13) =631a(14) =713a(15) =731a(16) =813a(17) =831a(18) =913a(19) =931a(20) =1013a(21) =1031a(22) =1113a(23) =1130a(24) =1213a(25) =1231a(26) =1300a(27) =1413a(28) =1431a(29) =1513