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

Terms

a(0) =1a(1) =6a(2) =66a(3) =666a(4) =6306a(5) =58026a(6) =527346a(7) =4766586a(8) =42981186a(9) =387158346a(10) =3485735826a(11) =31376865306a(12) =282412759266