Numbers with digits in ascending order that differ exactly by 1.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =6a(6) =7a(7) =8a(8) =9a(9) =12a(10) =23a(11) =34a(12) =45a(13) =56a(14) =67a(15) =78a(16) =89a(17) =123a(18) =234a(19) =345a(20) =456a(21) =567a(22) =678a(23) =789a(24) =1234a(25) =2345a(26) =3456a(27) =4567a(28) =5678a(29) =6789