a(n) = 7*(10^n - 1).

Terms

a(0) =0a(1) =63a(2) =693a(3) =6993a(4) =69993a(5) =699993a(6) =6999993a(7) =69999993a(8) =699999993a(9) =6999999993a(10) =69999999993a(11) =699999999993