a(n) = T(2n,n), T given by A027157.

Terms

a(0) =1a(1) =3a(2) =24a(3) =76a(4) =672a(5) =2208a(6) =20224a(7) =67776a(8) =632320a(9) =2144768a(10) =20238336a(11) =69203968a(12) =658079744a(13) =2263351296a(14) =21643526144a(15) =74764042240a(16) =717975060480