G.f. satisfies A(x) = x + ( Sum_{n>=1} A(x^n) )^2.

Terms

a(0) =1a(1) =1a(2) =4a(3) =14a(4) =52a(5) =195a(6) =774a(7) =3140a(8) =13118a(9) =55861a(10) =241988a(11) =1062411a(12) =4718380a(13) =21156811a(14) =95652842a(15) =435553638a(16) =1995707806a(17) =9194770161a(18) =42570402238a(19) =197957907525a(20) =924157498638