8^n - 3^n + 1.

Terms

a(0) =1a(1) =6a(2) =56a(3) =486a(4) =4016a(5) =32526a(6) =261416a(7) =2094966a(8) =16770656a(9) =134198046a(10) =1073682776a(11) =8589757446a(12) =68718945296a(13) =549754219566