E.g.f. x(1-x)^2/(1-3x+x^2).

Terms

a(0) =0a(1) =1a(2) =2a(3) =18a(4) =192a(5) =2520a(6) =39600a(7) =725760a(8) =15200640a(9) =358162560a(10) =9376819200a(11) =270037152000