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

Terms

a(0) =1a(1) =1a(2) =4a(3) =18a(4) =96a(5) =551a(6) =3332a(7) =20906a(8) =134820a(9) =888151a(10) =5951096a(11) =40432550a(12) =277892604a(13) =1928668910a(14) =13497833600a(15) =95150192558a(16) =674993798716