G.f. satisfies: A(x) = x + A((x+x^2)*A(x)) with A(0)=0.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =26a(6) =72a(7) =205a(8) =597a(9) =1770a(10) =5329a(11) =16253a(12) =50112a(13) =155939a(14) =489111a(15) =1544723a(16) =4908164a(17) =15678715a(18) =50323541a(19) =162213311a(20) =524895810a(21) =1704407999a(22) =5552027379a(23) =18137964251a(24) =59412854411a(25) =195090277189a(26) =642056206297