10^n+2^n-1.

Terms

a(0) =1a(1) =11a(2) =103a(3) =1007a(4) =10015a(5) =100031a(6) =1000063a(7) =10000127a(8) =100000255a(9) =1000000511a(10) =10000001023a(11) =100000002047