2nd differences of factorial numbers.

Terms

a(0) =1a(1) =3a(2) =14a(3) =78a(4) =504a(5) =3720a(6) =30960a(7) =287280a(8) =2943360a(9) =33022080a(10) =402796800a(11) =5308934400a(12) =75203251200