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

Terms

a(0) =1a(1) =2a(2) =7a(3) =28a(4) =123a(5) =572a(6) =2769a(7) =13806a(8) =70414a(9) =365636a(10) =1926505a(11) =10273870a(12) =55349155a(13) =300783420a(14) =1646828655a(15) =9075674700a(16) =50304255210a(17) =280248358964