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

Terms

a(0) =1a(1) =0a(2) =1a(3) =3a(4) =13a(5) =57a(6) =265a(7) =1273a(8) =6281a(9) =31634a(10) =161985a(11) =840795a(12) =4413937a(13) =23395376a(14) =125028541a(15) =672958929a(16) =3644868105a(17) =19850452482a(18) =108639736105a(19) =597190462341