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A226493
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Closed walks of length n in K_4 graph.
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2
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0, 12, 24, 84, 240, 732, 2184, 6564, 19680, 59052, 177144, 531444, 1594320, 4782972, 14348904, 43046724, 129140160, 387420492, 1162261464, 3486784404, 10460353200, 31381059612, 94143178824, 282429536484, 847288609440, 2541865828332, 7625597484984, 22876792454964
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OFFSET
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1,2
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COMMENTS
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REFERENCES
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Mike Krebs and Tony Shaheen, Expander Families and Cayley Graphs, Oxford University Press, Inc. 2011
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LINKS
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FORMULA
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a(n) = 3*(-1)^n + 3^n = 12*A015518(n-1).
G.f.: 12*x^2 / ( (1+x)*(1-3*x) ). - R. J. Mathar, Jun 29 2013
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MATHEMATICA
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Table[3 (-1)^k + 3^k, {k, 30}]
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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