T(2n,n-1), T given by A026692.

Terms

a(0) =1a(1) =4a(2) =24a(3) =89a(4) =507a(5) =1913a(6) =10832a(7) =41485a(8) =234997a(9) =909772a(10) =5161736a(11) =20142456a(12) =114475100a(13) =449409816a(14) =2558062376a(15) =10089877429a(16) =57509594605a(17) =227694240418