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

Terms

a(0) =1a(1) =2a(2) =0a(3) =6a(4) =-2a(5) =38a(6) =-32a(7) =314a(8) =-436a(9) =3014a(10) =-5732a(11) =31954a(12) =-74934a(13) =363642a(14) =-983868a(15) =4360230a(16) =-13021586a(17) =54374950a(18) =-173933428a(19) =698713298a(20) =-2345075002a(21) =9189017010a(22) =-31903354068a(23) =123070336590a(24) =-437701811100