a(n) = n! * n(n-1)/4.

Terms

a(0) =0a(1) =0a(2) =1a(3) =9a(4) =72a(5) =600a(6) =5400a(7) =52920a(8) =564480a(9) =6531840a(10) =81648000a(11) =1097712000a(12) =15807052800a(13) =242853811200