a(n) = (5*10^n - 41)/9 for n > 0.

Terms

a(0) =1a(1) =51a(2) =551a(3) =5551a(4) =55551a(5) =555551a(6) =5555551a(7) =55555551a(8) =555555551a(9) =5555555551a(10) =55555555551a(11) =555555555551