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