a(n) = (7*8^n + 2*(-1)^n)/9.

Terms

a(0) =1a(1) =6a(2) =50a(3) =398a(4) =3186a(5) =25486a(6) =203890a(7) =1631118a(8) =13048946a(9) =104391566a(10) =835132530a(11) =6681060238a(12) =53448481906a(13) =427587855246