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

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =10a(6) =26a(7) =71a(8) =198a(9) =562a(10) =1616a(11) =4698a(12) =13786a(13) =40784a(14) =121516a(15) =364341a(16) =1098522a(17) =3328713a(18) =10131858a(19) =30963944a(20) =94975810a(21) =292291370a(22) =902277354a(23) =2793028146a(24) =8668118364a(25) =26965143756a(26) =84068366948a(27) =262631106850a(28) =822019561552