a(n) = 2n*a(n-1) - (n-1)^2*a(n-2).

Terms

a(0) =0a(1) =1a(2) =4a(3) =20a(4) =124a(5) =920a(6) =7940a(7) =78040a(8) =859580a(9) =10477880a(10) =139931620a(11) =2030707640a(12) =31805257340a(13) =534514790680