T(2n,n), T given by A026703.

Terms

a(0) =1a(1) =3a(2) =13a(3) =61a(4) =293a(5) =1421a(6) =6925a(7) =33839a(8) =165621a(9) =811431a(10) =3978065a(11) =19511079a(12) =95723669a(13) =469727963a(14) =2305345429a(15) =11315403365a(16) =55543851357a(17) =272662287413