G.f. satisfies A(x) = 1 + x*(1 + x*A(x)^3)^2.

Terms

a(0) =1a(1) =1a(2) =2a(3) =7a(4) =24a(5) =95a(6) =386a(7) =1641a(8) =7150a(9) =31844a(10) =144216a(11) =662228a(12) =3076044a(13) =14427582a(14) =68235078a(15) =325049475a(16) =1558212804a(17) =7511319253a(18) =36387218312a(19) =177050945886a(20) =864912345340