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

Terms

a(0) =1a(1) =2a(2) =4a(3) =24a(4) =32a(5) =320a(6) =320a(7) =4480a(8) =3584a(9) =64512a(10) =43008a(11) =946176a(12) =540672a(13) =14057472a(14) =7028736a(15) =210862080a(16) =93716480a(17) =3186360320a(18) =1274544128a(19) =48432676864a(20) =17611882496a(21) =739699064832a(22) =246566354944