a(n) = 10^n - 7^n.

Terms

a(0) =0a(1) =3a(2) =51a(3) =657a(4) =7599a(5) =83193a(6) =882351a(7) =9176457a(8) =94235199a(9) =959646393a(10) =9717524751a(11) =98022673257a(12) =986158712799