T(2n-1,n), where T is the array defined in A025564.

Terms

a(0) =1a(1) =4a(2) =22a(3) =120a(4) =665a(5) =3732a(6) =21153a(7) =120835a(8) =694590a(9) =4013088a(10) =23284424a(11) =135580865a(12) =791862354a(13) =4637009300a(14) =27215510265a(15) =160053426720a(16) =942939231825