Number of chess tableaux with n cells.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =4a(5) =6a(6) =12a(7) =20a(8) =48a(9) =84a(10) =216a(11) =408a(12) =1104a(13) =2280a(14) =6288a(15) =14128a(16) =40256a(17) =96240a(18) =287904a(19) =714016a(20) =2246592a(21) =5750112a(22) =18900672a(23) =49973568a(24) =169592576a(25) =466175808a(26) =1618212224a(27) =4637091200a(28) =16393123072a(29) =48926588544