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

Terms

a(0) =0a(1) =2a(2) =8a(3) =36a(4) =192a(5) =1200a(6) =8640a(7) =70560a(8) =645120a(9) =6531840a(10) =72576000a(11) =878169600a(12) =11496038400a(13) =161902540800