a(n) = a(n-1) + a(n - 1 minus the number of terms of a(k) == (mod 6) so far).

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =6a(6) =11a(7) =17a(8) =28a(9) =39a(10) =50a(11) =89a(12) =139a(13) =189a(14) =239a(15) =378a(16) =428a(17) =667a(18) =906a(19) =1284a(20) =1712a(21) =2618a(22) =3046a(23) =3952a(24) =5664a(25) =6948a(26) =9994a(27) =12612a(28) =15658a(29) =18276