a(n) = 8*(10^n-5).

Terms

a(0) =40a(1) =760a(2) =7960a(3) =79960a(4) =799960a(5) =7999960a(6) =79999960a(7) =799999960a(8) =7999999960a(9) =79999999960a(10) =799999999960