a(n) = n!*(n+2)!/2.A010791a(n) = n!*(n+2)!/2.Terms a(0) =1a(1) =3a(2) =24a(3) =360a(4) =8640a(5) =302400a(6) =14515200a(7) =914457600a(8) =73156608000External referencesoeis: A010791