T(2n,n), where T is the array defined in A024996.

Terms

a(0) =1a(1) =2a(2) =5a(3) =24a(4) =133a(5) =736a(6) =4135a(7) =23452a(8) =134043a(9) =770864a(10) =4455462a(11) =25859380a(12) =150615223a(13) =879876040a(14) =5153445895a(15) =30251941860a(16) =177938418225