a(n) = binomial(n,2) * !n.

Terms

a(0) =0a(1) =0a(2) =2a(3) =12a(4) =60a(5) =340a(6) =2310a(7) =18354a(8) =165592a(9) =1664424a(10) =18410130a(11) =222085270a(12) =2901011124a(13) =40790592492a(14) =614247917374