a(n) = 2*a(n-1) - 2*(n-2)*a(n-2), with a(0)=1, a(1)=2.

Terms

a(0) =1a(1) =2a(2) =4a(3) =4a(4) =-8a(5) =-40a(6) =-16a(7) =368a(8) =928a(9) =-3296a(10) =-21440a(11) =16448a(12) =461696a(13) =561536a(14) =-9957632a(15) =-34515200a(16) =209783296a(17) =1455022592a(18) =-3803020288a(19) =-57076808704a(20) =22755112960