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 A023430 #19 Feb 03 2025 09:36:34
%S A023430 1,1,1,1,1,1,1,1,2,4,7,11,17,27,44,72,118,194,320,528,871,1439,2385,
%T A023430 3965,6605,11017,18399,30771,51538,86440,145165,244085,410890,692442,
%U A023430 1168114,1972470,3333834,5639888,9549311,16181931,27442827,46575013
%N A023430 Generalized Catalan Numbers x^4*A(x)^2 -(1-x+x^4+x^5+x^6+x^7)*A(x) + 1 =0.
%F A023430 G.f. A(x) satisfies: A(x) = (1 + x^4 * A(x)^2) / (1 - x + x^4 + x^5 + x^6 + x^7). - _Ilya Gutkovskiy_, Jul 20 2021
%p A023430 A023430 := proc(n)
%p A023430 option remember;
%p A023430 if n = 0 then
%p A023430 1;
%p A023430 else
%p A023430 procname(n-1)+add(procname(k)*procname(n-4-k),k=4..n-4) ;
%p A023430 end if;
%p A023430 end proc: # _R. J. Mathar_, May 01 2015
%t A023430 Clear[ a ]; a[ 0 ]=1; a[ n_Integer ] := a[ n ]=a[ n-1 ]+Sum[ a[ k ]*a[ n-4-k ], {k, 4, n-4} ];
%Y A023430 Cf. A000108, A001006, A004148, A006318.
%K A023430 nonn,easy
%O A023430 0,9
%A A023430 _Olivier Gérard_
%E A023430 More terms from _Sean A. Irvine_, Jun 04 2019