a(n) = 10^n+8^n-1.

Terms

a(0) =1a(1) =17a(2) =163a(3) =1511a(4) =14095a(5) =132767a(6) =1262143a(7) =12097151a(8) =116777215a(9) =1134217727a(10) =11073741823a(11) =108589934591