a(n) = (4*n + 1)*n!.

Terms

a(0) =1a(1) =5a(2) =18a(3) =78a(4) =408a(5) =2520a(6) =18000a(7) =146160a(8) =1330560a(9) =13426560a(10) =148780800a(11) =1796256000a(12) =23471078400a(13) =330032102400