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

Terms

a(0) =1a(1) =3a(2) =9a(3) =31a(4) =105a(5) =363a(6) =1249a(7) =4319a(8) =14913a(9) =51539a(10) =178057a(11) =615279a(12) =2125929a(13) =7345883a(14) =25382305a(15) =87704607a(16) =303048289a(17) =1047133859a(18) =3618196393a(19) =12502080287a(20) =43198864521a(21) =149266526667a(22) =515765751745