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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =19a(5) =64a(6) =228a(7) =841a(8) =3181a(9) =12277a(10) =48156a(11) =191400a(12) =769168a(13) =3120044a(14) =12758080a(15) =52533265a(16) =217637308a(17) =906511243a(18) =3793989118a(19) =15947205096a(20) =67290484581a(21) =284934164506