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 A001508 a(n) is the number of c-nets with n+1 vertices and 2n+2 edges, n >= 1. (Formerly M4918 N2111) 3
 0, 0, 0, 0, 13, 252, 3740, 51300, 685419, 9095856, 120872850, 1614234960, 21697730835, 293695935764, 4003423965684, 54944523689692, 758990230992175, 10548884795729280, 147458773053913268, 2072369440050644208, 29271357456284966994 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 REFERENCES N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Gheorghe Coserea, Table of n, a(n) for n = 1..204 R. C. Mullin and P. J. Schellenberg, The enumeration of c-nets via triangulations, J. Combin. Theory, 4 (1968), 259-276. FORMULA a(n) = A290326(n+2,n). - Gheorghe Coserea, Jul 28 2017 PROG (PARI) A290326(n, k) = {   if (n < 3 || k < 3, return(0));   sum(i=0, k-1, sum(j=0, n-1,      (-1)^((i+j+1)%2) * binomial(i+j, i)*(i+j+1)*(i+j+2)/2*      (binomial(2*n, k-i-1) * binomial(2*k, n-j-1) -       4 * binomial(2*n-1, k-i-2) * binomial(2*k-1, n-j-2)))); }; vector(21, n, A290326(n+2, n)) \\ Gheorghe Coserea, Jul 28 2017 CROSSREFS Cf. A290326. Sequence in context: A126422 A286878 A106738 * A157946 A321849 A034242 Adjacent sequences:  A001505 A001506 A001507 * A001509 A001510 A001511 KEYWORD nonn AUTHOR EXTENSIONS Corrected and extended by Sean A. Irvine, Sep 29 2015 Name changed by Gheorghe Coserea, Jul 23 2017 STATUS approved

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Last modified January 18 23:05 EST 2019. Contains 319282 sequences. (Running on oeis4.)