G.f. satisfies A(x) = 1 + x^2*A(x)^4*(1 + x*A(x)).

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =4a(5) =9a(6) =27a(7) =78a(8) =231a(9) =715a(10) =2193a(11) =6954a(12) =21999a(13) =70840a(14) =228896a(15) =746650a(16) =2447757a(17) =8072208a(18) =26745627a(19) =89002364a(20) =297344960a(21) =996865397a(22) =3352918429a(23) =11310307593a(24) =38256171642a(25) =129718262583a(26) =440855654827