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A177485
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G.f.: (1+x+x^3+x^5)/( (1-x^2+x^3)*(1-x-x^3) ).
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2
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1, 2, 3, 5, 7, 11, 15, 23, 32, 49, 69, 105, 149, 225, 321, 482, 691, 1033, 1487, 2215, 3199, 4751, 6880, 10193, 14793, 21873, 31801, 46945, 68353, 100770, 146899, 216333, 315671, 464467, 678287, 997287, 1457344, 2141473, 3131021, 4598617, 6726509, 9875521
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OFFSET
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0,2
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COMMENTS
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This counts independent sets in certain graphs.
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LINKS
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EXAMPLE
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For n=4, a(4)=7 because the graph is a cycle, and the independent sets are the empty set, {1}, {2}, {3}, {4}, {1,3} and {2,4}.
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MATHEMATICA
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CoefficientList[Series[(1+x+x^3+x^5)/( (1-x^2+x^3)*(1-x-x^3) ), {x, 0, 40}], x] (* Vaclav Kotesovec, Aug 25 2014 *)
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PROG
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(PARI) Vec((1+x+x^3+x^5)/((1-x^2+x^3)*(1-x-x^3)) + O(x^50)) \\ Michel Marcus, May 24 2015
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Signy Olafsdottir (signy06(AT)ru.is), May 09 2010
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EXTENSIONS
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STATUS
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approved
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