A006657 - OEIS

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A006657

Number of closed meanders with 2 components and 2n bridges.
(Formerly M2037)

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