Bisection of A138540.

Terms

a(0) =1a(1) =1a(2) =3a(3) =15a(4) =104a(5) =909a(6) =9449a(7) =112398a(8) =1489410a(9) =21562086a(10) =336086022a(11) =5577242292a(12) =97671172836