a(n) = 8*(10^n - 3).

Terms

a(0) =56a(1) =776a(2) =7976a(3) =79976a(4) =799976a(5) =7999976a(6) =79999976a(7) =799999976a(8) =7999999976a(9) =79999999976a(10) =799999999976