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

Terms

a(0) =0a(1) =72a(2) =792a(3) =7992a(4) =79992a(5) =799992a(6) =7999992a(7) =79999992a(8) =799999992a(9) =7999999992a(10) =79999999992a(11) =799999999992