a(n) = A027144(2n-1, n-1).

Terms

a(0) =1a(1) =6a(2) =20a(3) =152a(4) =528a(5) =4416a(6) =15488a(7) =135552a(8) =477440a(9) =4289536a(10) =15144960a(11) =138407936a(12) =489431040a(13) =4526702592a(14) =16024403968a(15) =149528084480a(16) =529747476480