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 A226493 Closed walks of length n in K_4 graph. 2
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Essentially the same as A218034. REFERENCES Mike Krebs and Tony Shaheen, Expander Families and Cayley Graphs, Oxford University Press, Inc. 2011 LINKS K. Böhmová, C. Dalfó, C. Huemer, On cyclic Kautz digraphs, Preprint 2016. Cristina Dalfó, From subKautz digraphs to cyclic Kautz digraphs, arXiv:1709.01882 [math.CO], 2017. C. Dalfó, The spectra of subKautz and cyclic Kautz digraphs, Linear Algebra and its Applications, 531 (2017), p. 210-219. Index entries for linear recurrences with constant coefficients, signature (2,3). FORMULA 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 MATHEMATICA Table[3 (-1)^k + 3^k, {k, 30}] PROG (PARI) a(n) = { 3*(-1)^n + 3^n } \\ Andrew Howroyd, Sep 11 2019 CROSSREFS Column k=4 of A106512. Cf. A218034. Sequence in context: A120360 A120356 A109745 * A051385 A290304 A289335 Adjacent sequences:  A226490 A226491 A226492 * A226494 A226495 A226496 KEYWORD nonn,easy AUTHOR Gustavo Gordillo, Jun 09 2013 STATUS approved

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Last modified February 16 16:00 EST 2020. Contains 331961 sequences. (Running on oeis4.)