a(n) = Product_{k=0..n-1} (n-4*k).

Terms

a(0) =1a(1) =1a(2) =-4a(3) =15a(4) =0a(5) =-1155a(6) =20160a(7) =-208845a(8) =0a(9) =68139225a(10) =-2075673600a(11) =34976316375a(12) =0a(16) =0a(20) =0