a(n) = [x^n] ((1 - x)/(1 - x + x^2))^n.

Terms

a(0) =1a(1) =0a(2) =-2a(3) =-3a(4) =6a(5) =25a(6) =1a(7) =-147a(8) =-218a(9) =591a(10) =2223a(11) =-484a(12) =-14871a(13) =-18759a(14) =68353a(15) =222697a(16) =-116058a(17) =-1629671a(18) =-1656989a(19) =8275203a(20) =23266031a(21) =-20154144a(22) =-184550412a(23) =-141418628a(24) =1019061001a(25) =2468408775a(26) =-3122976521a(27) =-21213927840a(28) =-10837119735a(29) =126256071125