a(n) = T(n,2n-9), T given by A027023.

Terms

a(0) =1a(1) =3a(2) =9a(3) =31a(4) =105a(5) =355a(6) =1197a(7) =4011a(8) =13329a(9) =43883a(10) =143105a(11) =462391a(12) =1481229a(13) =4707743a(14) =14856441a(15) =46585671a(16) =145253757a(17) =450624055a(18) =1391743825a(19) =4281348119a(20) =13124142489a(21) =40105164499a(22) =122213161617a(23) =371496978671