a(n) = 8*(10^n - 1)/9.

Terms

a(0) =0a(1) =8a(2) =88a(3) =888a(4) =8888a(5) =88888a(6) =888888a(7) =8888888a(8) =88888888a(9) =888888888a(10) =8888888888a(11) =88888888888a(12) =888888888888