3^n concatenated with itself.

Terms

a(0) =11a(1) =33a(2) =99a(3) =2727a(4) =8181a(5) =243243a(6) =729729a(7) =21872187a(8) =65616561a(9) =1968319683a(10) =5904959049a(11) =177147177147a(12) =531441531441