a(n) = 10^n - 5^n.

Terms

a(0) =0a(1) =5a(2) =75a(3) =875a(4) =9375a(5) =96875a(6) =984375a(7) =9921875a(8) =99609375a(9) =998046875a(10) =9990234375a(11) =99951171875a(12) =999755859375