T(2n,n+4), T given by A026769.

Terms

a(0) =1a(1) =10a(2) =67a(3) =380a(4) =1978a(5) =9814a(6) =47391a(7) =225590a(8) =1067527a(9) =5051454a(10) =24001979a(11) =114858924a(12) =554704282a(13) =2707092726a(14) =13359365962a(15) =66678605418a(16) =336519708452