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

Terms

a(0) =1a(1) =2a(2) =4a(3) =4a(4) =0a(5) =-4a(6) =0a(7) =8a(8) =0a(9) =-20a(10) =0a(11) =56a(12) =0a(13) =-168a(14) =0a(15) =528a(16) =0a(17) =-1716a(18) =0a(19) =5720a(20) =0a(21) =-19448a(22) =0a(23) =67184a(24) =0a(25) =-235144a(26) =0a(27) =832048a(28) =0a(29) =-2971600