a(n) = T(n,n), array T given by A048472.

Terms

a(0) =1a(1) =3a(2) =13a(3) =49a(4) =161a(5) =481a(6) =1345a(7) =3585a(8) =9217a(9) =23041a(10) =56321a(11) =135169a(12) =319489a(13) =745473a(14) =1720321a(15) =3932161a(16) =8912897a(17) =20054017a(18) =44826625a(19) =99614721a(20) =220200961a(21) =484442113a(22) =1061158913a(23) =2315255809a(24) =5033164801a(25) =10905190401a(26) =23555211265a(27) =50734301185a(28) =108984795137a(29) =233538846721