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Search: id:A006664
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| A006664 |
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Number of irreducible systems of meanders.
(Formerly M1871)
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+0
5
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| 1, 1, 2, 8, 46, 322, 2546, 21870, 199494, 1904624, 18846714, 191955370, 2002141126, 21303422480, 230553207346, 2531848587534, 28159614749270, 316713536035464, 3597509926531778, 41225699113145888, 476180721050626814, 5539597373695447322, 64863295574835126394, 763984568163192551672, 9047263176444565467566
(list; graph; listen)
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OFFSET
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0,3
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
V. I. Arnol'd, A branched covering of CP^2->S^4, hyperbolicity and projective topology [ Russian ], Sibir. Mat. Zhurn., 29 (No. 2, 1988), 36-47 = Siberian Math. J., 29 (1988), 717-725.
S. K. Lando and A. K. Zvonkin "Plane and projective meanders", S\'{e}ries Formelles et Combinatoire Alg\'{e}brique. Laboratoire Bordelais de Recherche Informatique, Universit\'{e} Bordeaux I, 1991, pp. 287-303.
S. K. Lando and A. K. Zvonkin, "Meanders", Selecta Mathematica Sovietica Vol. 11, Number 2, pp. 117-144, 1992.
S. K. Lando and A. K. Zvonkin, "Plane and projective meanders", Theoretical Computer Science Vol. 117, pp. 227-241, 1993.
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FORMULA
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A(x^2)=S(x^2)#inv(x*S(x^2)) where # is functional composition, S(x) is g.f. of A001246 (squares of Catalan numbers) and inv(.) is functional inverse. A(x) consists of even-numbered terms of A(x^2), odd terms of which are 0. - Doug McIlroy (doug(AT)cs.dartmouth.edu), Mar 22 2006
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CROSSREFS
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Sequence in context: A144164 A003091 A119501 this_sequence A141117 A145844 A005840
Adjacent sequences: A006661 A006662 A006663 this_sequence A006665 A006666 A006667
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KEYWORD
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nonn,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Simon Plouffe (simon.plouffe(AT)gmail.com)
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EXTENSIONS
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More terms from Doug McIlroy (doug(AT)cs.dartmouth.edu), Mar 22 2006
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