2^(n-2)*n*(n+2)!/3.

Terms

a(0) =0a(1) =1a(2) =16a(3) =240a(4) =3840a(5) =67200a(6) =1290240a(7) =27095040a(8) =619315200a(9) =15328051200a(10) =408748032000