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

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =7a(5) =15a(6) =39a(7) =103a(8) =267a(9) =719a(10) =1975a(11) =5447a(12) =15199a(13) =42863a(14) =121647a(15) =347455a(16) =998559a(17) =2884143a(18) =8367599a(19) =24377503a(20) =71282351a(21) =209132511a(22) =615447711a(23) =1816255583a(24) =5373748287a(25) =15937008575a(26) =47368376255a(27) =141075930495a(28) =420957812863