a(n) = n^2*(n-2)^2*(n-4)^2*...*(1 or 2)^2.

Terms

a(0) =1a(1) =1a(2) =4a(3) =9a(4) =64a(5) =225a(6) =2304a(7) =11025a(8) =147456a(9) =893025a(10) =14745600a(11) =108056025a(12) =2123366400a(13) =18261468225a(14) =416179814400