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

Terms

a(0) =1a(1) =6a(2) =30a(3) =168a(4) =1080a(5) =7920a(6) =65520a(7) =604800a(8) =6168960a(9) =68947200a(10) =838252800a(11) =11017036800a(12) =155675520000