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

Terms

a(0) =1a(1) =8a(2) =71a(3) =638a(4) =5741a(5) =51668a(6) =465011a(7) =4185098a(8) =37665881a(9) =338992928a(10) =3050936351a(11) =27458427158a(12) =247125844421