G.f.: A(x) = x + A(-x)^2.

Terms

a(0) =1a(1) =1a(2) =-2a(3) =-3a(4) =10a(5) =18a(6) =-68a(7) =-131a(8) =530a(9) =1062a(10) =-4476a(11) =-9198a(12) =39844a(13) =83332a(14) =-368136a(15) =-780003a(16) =3497058a(17) =7483806a(18) =-33940940a(19) =-73210874a(20) =335103340a(21) =727473084a(22) =-3355045304a(23) =-7322240718a(24) =33982884884a(25) =74498594492a(26) =-347600543192a(27) =-764936992764