T(2n,n), array T given by A047020.

Terms

a(0) =1a(1) =1a(2) =3a(3) =19a(4) =99a(5) =624a(6) =3684a(7) =23379a(8) =144877a(9) =927084a(10) =5882776a(11) =37925111a(12) =243908212a(13) =1582102118a(14) =10261788552a(15) =66893579077a(16) =436419943039