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 A186812 #24 Feb 13 2023 09:00:32
%S A186812 1,1,3,8,21,53,135,346,886,2266,5796,14828,37935,97047,248269,635134,
%T A186812 1624833,4156729,10633949,27204296,69595384,178042372,455476844,
%U A186812 1165223500,2980932677,7625970145,19509135875,49909241100,127680301337,326638093273,835621805859
%N A186812 Expansion of 1/(1-x^6-3*x^5-4*x^4-3*x^3-2*x^2-x).
%H A186812 Vladimir Kruchinin, <a href="http://arxiv.org/abs/1009.2565">Composition of ordinary generating functions</a>, arXiv:1009.2565 [math.CO], 2010.
%H A186812 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (1,2,3,4,3,1)
%F A186812 a(n+1) = sum(m=1..n, sum(k=m..n, binomial(k,n-k) *sum(j=0..m, binomial(m,j) *binomial(j,k-3*m+2*j)))).
%t A186812 CoefficientList[Series[1/(1-x^6-3x^5-4x^4-3x^3-2x^2-x),{x,0,30}],x] (* or *) LinearRecurrence[{1,2,3,4,3,1},{1,1,3,8,21,53},30] (* _Harvey P. Dale_, Aug 30 2014 *)
%K A186812 nonn,easy
%O A186812 0,3
%A A186812 _Vladimir Kruchinin_, Feb 28 2011
%E A186812 More terms from _Harvey P. Dale_, Aug 30 2014