a(n) = floor((n-1)!/n).

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =4a(5) =20a(6) =102a(7) =630a(8) =4480a(9) =36288a(10) =329890a(11) =3326400a(12) =36846276a(13) =444787200a(14) =5811886080a(15) =81729648000