Number of permutations of [2n] with n inversions.

Terms

a(0) =1a(1) =1a(2) =5a(3) =29a(4) =174a(5) =1068a(6) =6655a(7) =41926a(8) =266338a(9) =1703027a(10) =10947079a(11) =70673825a(12) =457927079a(13) =2976282415a(14) =19395654894a(15) =126688273871a(16) =829176461458