a(n) = (n^2-1)*n!/3.

A090672

a(n) = (n^2-1)*n!/3.

Terms

    a(0) =0a(1) =2a(2) =16a(3) =120a(4) =960a(5) =8400a(6) =80640a(7) =846720a(8) =9676800a(9) =119750400a(10) =1596672000a(11) =22832409600a(12) =348713164800

External references