This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A308030 #9 Aug 08 2019 21:07:27 %S A308030 1,1,1,1,2,4,8,18,45,122,350,1052,3313,10933,37739,135865,508545, %T A308030 1973717,7926795,32895354,140894024,622160220,2829323210,13235526027, %U A308030 63620528705,313909404040,1588405927920,8235905545581,43724990832997,237527663672208,1319398402129845 %N A308030 G.f. A(x) satisfies: A(x) = x + x^2 + x^3 * (1 + A(A(x))). %C A308030 Shifts left 3 places under COMPOSE transform. %t A308030 terms = 31; A[_] = 0; Do[A[x_] = x + x^2 + x^3 (1 + A[A[x]]) + O[x]^(terms + 1) // Normal, terms + 1]; Rest[CoefficientList[A[x], x]] %t A308030 Nest[x + x^2 + x^3 + x^3 (# /. x -> #) &, O[x], 20][[3]] (* _Vladimir Reshetnikov_, Aug 08 2019 *) %Y A308030 Cf. A030266, A030277, A308031, A308032. %K A308030 nonn %O A308030 1,5 %A A308030 _Ilya Gutkovskiy_, May 10 2019