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 A109499 Number of closed walks of length n on the complete graph on 5 nodes from a given node. 17
 1, 0, 4, 12, 52, 204, 820, 3276, 13108, 52428, 209716, 838860, 3355444, 13421772, 53687092, 214748364, 858993460, 3435973836, 13743895348, 54975581388, 219902325556, 879609302220, 3518437208884, 14073748835532 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Ji Young Choi, A Generalization of Collatz Functions and Jacobsthal Numbers, J. Int. Seq., Vol. 21 (2018), Article 18.5.4. Index entries for linear recurrences with constant coefficients, signature (3,4). FORMULA G.f.: (1 - 3*x)/(1 - 3*x - 4*x^2). a(n) = (4^n + 4*(-1)^n)/5. a(n+1) = 4*A015521(n). - Paul Curtz, Nov 01 2009 a(n) = 3*a(n-1) + 4*a(n-1). - G. C. Greubel, Dec 30 2017 a(n) = A108020((n - 1) / 2) = 'ccc...c' (n digits) in base 16, for odd n. - Georg Fischer, Mar 23 2019 E.g.f.: (exp(4*x) + 4*exp(-x))/5. - G. C. Greubel, Mar 23 2019 MATHEMATICA CoefficientList[Series[(1-3*x)/(1-3*x-4*x^2), {x, 0, 30}], x] (* or *) LinearRecurrence[{3, 4}, {1, 0}, 30] (* G. C. Greubel, Dec 30 2017 *) PROG (MAGMA) [(4^n + 4*(-1)^n)/5: n in [0..30]]; // Vincenzo Librandi, Aug 12 2011 (PARI) a(n)=(4^n+4*(-1)^n)/5 \\ Charles R Greathouse IV, Oct 01 2012 (Sage) [(4^n+4*(-1)^n)/5 for n in (0..30)] # G. C. Greubel, Mar 23 2019 (GAP) a:=[1, 0];; for n in [3..30] do a[n]:=3*a[n-1]+4*a[n-2]; od; a; # G. C. Greubel, Mar 23 2019 CROSSREFS Cf. A108020 (bisection), A109502. Cf. A001045, A078008, A097073, A115341, A015518, A054878, A015521 (forms k=4^n-k). - Vladimir Joseph Stephan Orlovsky, Dec 11 2008 Sequence in context: A149411 A149412 A259274 * A282587 A188230 A124006 Adjacent sequences:  A109496 A109497 A109498 * A109500 A109501 A109502 KEYWORD nonn,easy,walk AUTHOR Mitch Harris, Jun 30 2005 EXTENSIONS Corrected by Franklin T. Adams-Watters, Sep 18 2006 STATUS approved

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Last modified May 8 18:28 EDT 2021. Contains 343666 sequences. (Running on oeis4.)