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

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =17a(5) =54a(6) =177a(7) =600a(8) =2090a(9) =7418a(10) =26730a(11) =97556a(12) =359902a(13) =1339950a(14) =5028198a(15) =18998181a(16) =72214530a(17) =275961940a(18) =1059580185a(19) =4085690663a(20) =15814755274a(21) =61428318546a(22) =239358417367a(23) =935373031350