Number of bipartite partitions of n white objects and n black ones.

Terms

a(0) =1a(1) =2a(2) =9a(3) =31a(4) =109a(5) =339a(6) =1043a(7) =2998a(8) =8406a(9) =22652a(10) =59521a(11) =151958a(12) =379693a(13) =927622a(14) =2224235a(15) =5236586a(16) =12130780a(17) =27669593a(18) =62229990a(19) =138095696a(20) =302673029a(21) =655627975a(22) =1404599867a(23) =2977831389a(24) =6251060785a(25) =12999299705a(26) =26791990052a(27) =54750235190a(28) =110977389012