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

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =4a(6) =8a(7) =15a(8) =25a(9) =50a(10) =102a(11) =193a(12) =390a(13) =815a(14) =1645a(15) =3385a(16) =7141a(17) =14893a(18) =31196a(19) =66309a(20) =140752a(21) =299043a(22) =640367a(23) =1373929a(24) =2950006a(25) =6360976a(26) =13749865a(27) =29753891a(28) =64547097a(29) =140329453