Duplicate of A054663.

Terms

a(0) =1a(1) =2a(2) =8a(3) =30a(4) =124a(5) =516a(6) =2232a(7) =9750a(8) =43400a(9) =195248a(10) =887784a(11) =4068740a(12) =18780048a(13) =87191964