a(n) = a(n-1) - n*a(n-2); a(0) = a(1) = 1.

Terms

a(0) =1a(1) =1a(2) =-1a(3) =-4a(4) =0a(5) =20a(6) =20a(7) =-120a(8) =-280a(9) =800a(10) =3600a(11) =-5200a(12) =-48400a(13) =19200a(14) =696800a(15) =408800a(16) =-10740000a(17) =-17689600a(18) =175630400a(19) =511732800a(20) =-3000875200a(21) =-13747264000a(22) =52271990400a(23) =368459062400a(24) =-886068707200