G.f. satisfies A(x) = 1 + x^3*A(x)^2 / (1 - x*A(x)).

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =1a(5) =1a(6) =3a(7) =6a(8) =10a(9) =20a(10) =42a(11) =84a(12) =170a(13) =354a(14) =740a(15) =1549a(16) =3269a(17) =6945a(18) =14811a(19) =31711a(20) =68177a(21) =147091a(22) =318313a(23) =690837a(24) =1503351a(25) =3279445a(26) =7169907a(27) =15708485a(28) =34482475a(29) =75830981