T(2n,n), T given by A026714.

Terms

a(0) =1a(1) =3a(2) =13a(3) =63a(4) =319a(5) =1647a(6) =8583a(7) =44941a(8) =235913a(9) =1240173a(10) =6524919a(11) =34346785a(12) =180855499a(13) =952494047a(14) =5017037457a(15) =26428222177a(16) =139223327493a(17) =733452042061