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 A006469 Number of rooted genus-1 maps with 2 faces, n vertices and no isthmuses. (Formerly M4727) 1
 10, 79, 340, 1071, 2772, 6258, 12768, 24090, 42702, 71929, 116116, 180817, 273000, 401268, 576096, 810084, 1118226, 1518195, 2030644, 2679523, 3492412, 4500870, 5740800, 7252830, 9082710, 11281725, 13907124, 17022565, 20698576, 25013032, 30051648, 35908488 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Colin Barker, Table of n, a(n) for n = 1..1000 T. R. S. Walsh, A. B. Lehman, Counting rooted maps by genus. III: Nonseparable maps, J. Combinatorial Theory Ser. B 18 (1975), 222-259. Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1). FORMULA G.f.: x/(x-1)^7*(3*x^2-9*x-10), in Simon Plouffe Master thesis, Uqam 1992. From Colin Barker, Apr 22 2017: (Start) a(n) = (n*(474 + 1247*n + 1215*n^2 + 545*n^3 + 111*n^4 + 8*n^5)) / 360. a(n) = 7*a(n-1) - 21*a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7) for n>7. (End) PROG (PARI) Vec(x*(10 + 9*x - 3*x^2) / (1 - x)^7 + O(x^40)) \\ Colin Barker, Apr 22 2017 CROSSREFS Sequence in context: A222701 A283658 A160655 * A288630 A081905 A016138 Adjacent sequences:  A006466 A006467 A006468 * A006470 A006471 A006472 KEYWORD nonn,easy AUTHOR EXTENSIONS Name improved by Sean A. Irvine, Apr 21 2017 STATUS approved

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Last modified January 17 05:26 EST 2019. Contains 319207 sequences. (Running on oeis4.)