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 A287485 Number of independent vertex sets and vertex covers in the n-web graph. 0
 2, 20, 68, 304, 1232, 5168, 21408, 89088, 370112, 1538560, 6394368, 26577664, 110464512, 459127808, 1908282368, 7931445248, 32965660672, 137016012800, 569483091968, 2366956929024, 9837842644992, 40889273090048, 169949115056128, 706363785412608, 2935877583634432, 12202461910794240 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Eric Weisstein's World of Mathematics, Independent Vertex Set Eric Weisstein's World of Mathematics, Vertex Cover Eric Weisstein's World of Mathematics, Web Graph Index entries for linear recurrences with constant coefficients, signature (2,8,4). FORMULA G.f.: -2*x*(1 + 8*x + 6*x^2)/(-1 + 2*x + 8*x^2 + 4*x^3). a(n) = 2*a(n-1) + 8*a(n-2) + 4*a(n-3). MATHEMATICA Table[RootSum[-4 - 8 # - 2 #^2 + #^3 &, #^n &], {n, 20}] LinearRecurrence[{2, 8, 4}, {2, 20, 68}, 20] CoefficientList[Series[-2 (1 + 8 x + 6 x^2)/(-1 + 2 x + 8 x^2 + 4 x^3), {x, 0, 20}], x] (* Eric W. Weisstein, Sep 27 2017 *) PROG (PARI) Vec(-2*x*(1+8*x+6*x^2)/(-1+2*x+8*x^2+4*x^3) + O(x^30)) \\ Michel Marcus, Sep 27 2017 CROSSREFS Sequence in context: A183907 A216609 A226394 * A003283 A259110 A135188 Adjacent sequences:  A287482 A287483 A287484 * A287486 A287487 A287488 KEYWORD nonn,easy AUTHOR Eric W. Weisstein, May 25 2017 STATUS approved

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Last modified January 29 00:42 EST 2022. Contains 350670 sequences. (Running on oeis4.)