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

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =30a(5) =108a(6) =406a(7) =1577a(8) =6280a(9) =25499a(10) =105169a(11) =439388a(12) =1855636a(13) =7908909a(14) =33975250a(15) =146954693a(16) =639460707a(17) =2797384235a(18) =12295494109a(19) =54272825103a(20) =240480529815