a(n) = n! *((-1)^n + 2*n + 3)/4.

Terms

a(0) =1a(1) =1a(2) =4a(3) =12a(4) =72a(5) =360a(6) =2880a(7) =20160a(8) =201600a(9) =1814400a(10) =21772800a(11) =239500800a(12) =3353011200a(13) =43589145600a(14) =697426329600