a(n) = (2n+1)*n!.

Terms

a(0) =1a(1) =3a(2) =10a(3) =42a(4) =216a(5) =1320a(6) =9360a(7) =75600a(8) =685440a(9) =6894720a(10) =76204800a(11) =918086400a(12) =11975040000a(13) =168129561600