9^n - 3^n + 1.

Terms

a(0) =1a(1) =7a(2) =73a(3) =703a(4) =6481a(5) =58807a(6) =530713a(7) =4780783a(8) =43040161a(9) =387400807a(10) =3486725353a(11) =31380882463a(12) =282429005041