a(n) = Sum_{ k, k|n } 10^(k-1).

Terms

a(0) =1a(1) =11a(2) =101a(3) =1011a(4) =10001a(5) =100111a(6) =1000001a(7) =10001011a(8) =100000101a(9) =1000010011a(10) =10000000001a(11) =100000101111