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 A006657 Number of closed meanders with 2 components and 2n bridges. (Formerly M2037) 2
 2, 12, 84, 640, 5236, 45164, 406012, 3772008, 35994184, 351173328, 3490681428, 35253449296, 360946635312, 3739935635756, 39159200588780, 413836299216608, 4409705753032648, 47337525317450816, 511563350415103008 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 REFERENCES S. K. Lando and A. K. Zvonkin "Plane and projective meanders", Séries Formelles et Combinatoire Algébrique. Laboratoire Bordelais de Recherche Informatique, Université Bordeaux I, 1991, pp. 287-303. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Table of n, a(n) for n=2..20. P. Di Francesco, O. Golinelli and E. Guitter, Meander, folding and arch statistics, arXiv:hep-th/9506030, 1995. S. K. Lando and A. K. Zvonkin, Plane and projective meanders, Séries Formelles et Combinatoire Algébrique. Laboratoire Bordelais de Recherche Informatique, Université Bordeaux I, 1991, pp. 287-303. (Annotated scanned copy) MATHEMATICA A008828 = Import["https://oeis.org/A008828/b008828.txt", "Table"][[All, 2]]; a[n_] := A008828[[(n^2 - n + 4)/2]]; a /@ Range[2, 20] (* Jean-François Alcover, Sep 25 2019 *) CROSSREFS Cf. A005315. A column of triangle A008828. Sequence in context: A130464 A319326 A214765 * A105927 A316702 A235351 Adjacent sequences: A006654 A006655 A006656 * A006658 A006659 A006660 KEYWORD nonn,nice AUTHOR N. J. A. Sloane, Simon Plouffe EXTENSIONS a(13)-a(20) from Andrew Howroyd, Nov 22 2015 STATUS approved

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Last modified November 28 22:38 EST 2023. Contains 367422 sequences. (Running on oeis4.)