Trisection of A001317.

Terms

a(0) =1a(1) =15a(2) =85a(3) =771a(4) =4369a(5) =65535a(6) =327685a(7) =3342387a(8) =16843009a(9) =252645135a(10) =1431655765a(11) =12884901891a(12) =73014444049