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 A188580 #16 Dec 10 2012 03:07:50
%S A188580 1,5,25,125,625,3120,15580,77800,388500,1940000,9687520,48375280,
%T A188580 241565200,1206272000,6023600000,30079249920,150202748480,
%U A188580 750047481600,3745412320000,18702967200000,93394519000320,466371784007680,2328858730112000,11629312001280000,58071748137600000,289985162611998720,1448060325923962880,7230986194699366400
%N A188580 Number of words of length n over an alphabet of size 5 which do not contain a run of 5 identical letters.
%C A188580 This is the case M=5 of the general problem mentioned in A188714.
%H A188580 Vincenzo Librandi, <a href="/A188580/b188580.txt">Table of n, a(n) for n = 0..1000</a>
%F A188580 G.f.: (1+x+x^2+x^3+x^4)/(1-4*x-4*x^2-4*x^3-4*x^4).
%p A188580 See A188714.
%t A188580 CoefficientList[Series[(1 + x + x^2 + x^3 + x^4)/(1 - 4*x - 4*x^2 - 4*x^3 - 4*x^4), {x, 0, 40}], x] (* _Vincenzo Librandi_, Dec 09 2012 *)
%Y A188580 Cf. A040000, A121907, A188714.
%K A188580 nonn,easy
%O A188580 0,2
%A A188580 _N. J. A. Sloane_, Apr 09 2011