10^n+9^n-1.

Terms

a(0) =1a(1) =18a(2) =180a(3) =1728a(4) =16560a(5) =159048a(6) =1531440a(7) =14782968a(8) =143046720a(9) =1387420488a(10) =13486784400a(11) =131381059608