a(n) = 9^n-6^n+1.

Terms

a(0) =1a(1) =4a(2) =46a(3) =514a(4) =5266a(5) =51274a(6) =484786a(7) =4503034a(8) =41367106a(9) =377342794a(10) =3426318226a(11) =31018262554a(12) =280252754146