a(n) = 7*8^n-6*7^n.

Terms

a(0) =1a(1) =14a(2) =154a(3) =1526a(4) =14266a(5) =128534a(6) =1129114a(7) =9738806a(8) =82851706a(9) =697402454a(10) =5821341274a(11) =48265581686a(12) =397988613946