G.f. satisfies: A(x) = x + A(x*A(x)/(1-x)) with A(0)=0.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =13a(5) =36a(6) =104a(7) =311a(8) =955a(9) =2994a(10) =9542a(11) =30818a(12) =100633a(13) =331657a(14) =1101708a(15) =3684785a(16) =12398126a(17) =41936805a(18) =142520868a(19) =486400191a(20) =1666330558a(21) =5728305895a(22) =19754004806a(23) =68317426480a(24) =236893446915a(25) =823435684539