a(n) = 9^n-n^7.

Terms

a(0) =1a(1) =8a(2) =-47a(3) =-1458a(4) =-9823a(5) =-19076a(6) =251505a(7) =3959426a(8) =40949569a(9) =382637520a(10) =3476784401a(11) =31361572438a(12) =282393704673