a(n) = (4*9^n + (-1)^n)/5.

Terms

a(0) =1a(1) =7a(2) =65a(3) =583a(4) =5249a(5) =47239a(6) =425153a(7) =3826375a(8) =34437377a(9) =309936391a(10) =2789427521a(11) =25104847687a(12) =225943629185