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A006406
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Number of 2-connected planar maps with n edges (see reference for precise definition).
(Formerly M1195)
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3
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1, 1, 2, 4, 9, 24, 81, 274, 1071, 4357, 18416, 80040, 356109, 1610910, 7399114
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OFFSET
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3,3
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COMMENTS
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Equivalently, a(n) is the number of embeddings on the sphere of 2-connected planar graphs with n edges up to orientation preserving isomorphisms. - Andrew Howroyd, Mar 27 2021
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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).
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LINKS
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Table of n, a(n) for n=3..17.
Timothy R. Walsh, Generating nonisomorphic maps without storing them, SIAM J. Algebraic Discrete Methods 4 (1983), no. 2, 161-178.
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FORMULA
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a(n) = Sum_{k=3..n} A342059(k, n+2-k). - Andrew Howroyd, Mar 27 2021
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CROSSREFS
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Cf. A006402, A006404, A006407 (unsensed case), A342059.
Sequence in context: A210342 A137154 A098448 * A097656 A324148 A012936
Adjacent sequences: A006403 A006404 A006405 * A006407 A006408 A006409
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KEYWORD
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nonn,more
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AUTHOR
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N. J. A. Sloane
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EXTENSIONS
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a(11) and a(12) from Sean A. Irvine, Apr 02 2017
a(13)-a(17) from Andrew Howroyd, Mar 27 2021
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STATUS
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approved
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