a(n) = 4*10^n+1.

Terms

a(0) =5a(1) =41a(2) =401a(3) =4001a(4) =40001a(5) =400001a(6) =4000001a(7) =40000001a(8) =400000001a(9) =4000000001a(10) =40000000001a(11) =400000000001