a(n)=T(2n+1,n+1), where T is given by A048113.

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =18a(5) =60a(6) =204a(7) =720a(8) =2580a(9) =9408a(10) =34668a(11) =129024a(12) =483672a(13) =1824768a(14) =6919752a(15) =26357976a(16) =100778472a(17) =386591304a(18) =1487221056a(19) =5735785176a(20) =22170562656a(21) =85866332760a(22) =333151068528