G.f. A(x) satisfies A(x) = 1/( 1 + x*(1 - 4*x*A(x))^(1/2) ).

Terms

a(0) =1a(1) =-1a(2) =3a(3) =-5a(4) =17a(5) =-31a(6) =119a(7) =-211a(8) =937a(9) =-1483a(10) =8015a(11) =-10187a(12) =73369a(13) =-62193a(14) =713907a(15) =-234857a(16) =7358657a(17) =1881661a(18) =80117735a(19) =69295469a(20) =917837521a(21) =1334044075a(22) =11006114883a(23) =21830065899a(24) =137275956089a(25) =333858963899