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%I #9 Aug 07 2017 22:05:20
%S 1,3,4,11,16,24,43,75,130,218,375,644,1106,1893,3244,5563,9538,16350,
%T 28026,48046,82366,141199,242053,414948,711341,1219442,2090470,
%U 3583661,6143419,10531574,18054122,30949915,53056986,90954814,155922503,267295658,458221025
%N Number of irredundant sets in the n-cycle graph.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/CycleGraph.html">Cycle Graph</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/IrredundantSet.html">Irredundant Set</a>
%H <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (1, 1, 0, 1, 0, -1).
%F a(n) = a(n-1)+a(n-2)+a(n-4)-a(n-6).
%F G.f.: (x (1 + 2 x + 4 x^3 - 6 x^5))/(1 - x - x^2 - x^4 + x^6).
%t Table[RootSum[1 - #^2 - #^4 - #^5 + #^6 &, #^n &], {n, 20}]
%t LinearRecurrence[{1, 1, 0, 1, 0, -1}, {1, 3, 4, 11, 16, 24}, 20]
%t CoefficientList[Series[(1 + 2 x + 4 x^3 - 6 x^5)/(1 - x - x^2 - x^4 + x^6), {x, 0, 20}], x]
%K nonn,easy
%O 1,2
%A _Eric W. Weisstein_, Aug 04 2017
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