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

Terms

a(0) =1a(1) =1a(2) =2a(3) =8a(4) =26a(5) =56a(6) =194a(7) =832a(8) =2866a(9) =7904a(10) =30690a(11) =137000a(12) =497706a(13) =1491512a(14) =6041602a(15) =27557184a(16) =102985186a(17) =321675648a(18) =1333006018a(19) =6160815624a(20) =23426000186a(21) =75016874488a(22) =315357132994