G.f. A(x) satisfies: A(x) = x + x^2 + x^3 + x^4 * (1 + A(A(x))).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =4a(7) =8a(8) =16a(9) =34a(10) =78a(11) =195a(12) =523a(13) =1472a(14) =4284a(15) =12832a(16) =39608a(17) =126406a(18) =418276a(19) =1436230a(20) =5110170a(21) =18785417a(22) =71109917a(23) =276404921a(24) =1101234823a(25) =4493335194a(26) =18773200580a(27) =80320474041a(28) =351906635253