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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =10a(5) =33a(6) =72a(7) =236a(8) =572a(9) =1964a(10) =4800a(11) =16910a(12) =42354a(13) =150670a(14) =386992a(15) =1390176a(16) =3622696a(17) =13128940a(18) =34580568a(19) =126131776a(20) =335409928a(21) =1229708169a(22) =3295834080a(23) =12137093684a(24) =32738710652a(25) =121016095812a(26) =328220839472