a(n) = (n!/floor(1+n/2)!)^2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =9a(4) =16a(5) =400a(6) =900a(7) =44100a(8) =112896a(9) =9144576a(10) =25401600a(11) =3073593600a(12) =9032601600