a(n) = a(n-1) - 2*a(n-2) - 3*a(n-3) - ... - (n-1)*a(1), with a(1) = a(2) = 1, a(3) = -1.

Terms

a(0) =1a(1) =1a(2) =-1a(3) =-6a(4) =-11a(5) =-5a(6) =28a(7) =87a(8) =111a(9) =-46a(10) =-519a(11) =-1105a(12) =-812a(13) =2051a(14) =8003a(15) =12130a(16) =477a(17) =-43213a(18) =-107764a(19) =-106273a(20) =133575a(21) =716562a(22) =1269265a(23) =492135a(24) =-3436796a(25) =-10232533a(26) =-12529349a(27) =6701026a(28) =62284757a(29) =128290443