a(n) = (7*10^n - 61)/9 for n > 0.

Terms

a(0) =1a(1) =71a(2) =771a(3) =7771a(4) =77771a(5) =777771a(6) =7777771a(7) =77777771a(8) =777777771a(9) =7777777771a(10) =77777777771a(11) =777777777771