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

Terms

a(0) =1a(1) =1a(2) =4a(3) =36a(4) =144a(5) =3600a(6) =14400a(7) =705600a(8) =2822400a(9) =228614400a(10) =914457600a(11) =110649369600a(12) =442597478400