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

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =6a(5) =15a(6) =43a(7) =135a(8) =462a(9) =1708a(10) =6752a(11) =28302a(12) =125036a(13) =579709a(14) =2811084a(15) =14216095a(16) =74788529a(17) =408388370a(18) =2310191935a(19) =13514877249a(20) =81639455600a(21) =508524173808