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

Terms

a(0) =1a(1) =1a(2) =4a(3) =36a(4) =36a(5) =900a(6) =400a(7) =19600a(8) =4900a(9) =396900a(10) =63504a(11) =7683984a(12) =853776a(13) =144288144a(14) =11778624a(15) =2650190400a(16) =165636900a(17) =47869064100a(18) =2363904400a(19) =853369488400a(20) =34134779536a(22) =497634306624