a(n) = 9^n - 8^n - 7^n - 6^n + 3*5^n.

Terms

a(0) =1a(1) =3a(2) =7a(3) =33a(4) =643a(5) =11073a(6) =151867a(7) =1816713a(8) =19996963a(9) =208630833a(10) =2099398027a(11) =20597485593a(12) =198424412083