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

Terms

a(0) =1a(1) =18a(2) =199a(3) =1756a(4) =13624a(5) =97434a(6) =659549a(7) =4294814a(8) =27187126a(9) =168499288a(10) =1027595830a(11) =6188801692a(12) =36907274904a(13) =218380550880