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A006246
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Number of simple arrangements of pseudolines in the projective plane with an oriented marked cell; number of oriented abstract order types of n points (distinguishing mirror-symmetric copies)
(Formerly M0920)
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3
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1, 1, 1, 2, 3, 20, 242, 6405, 316835, 28627261, 4686329954
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listen;
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OFFSET
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1,4
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COMMENTS
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Previous name was: Number of primitive sorting networks on n elements.
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REFERENCES
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M. H. Klin et al., "2D-configurations and clique-cyclic orientations of the graphs L(K_p)", pages 149-162 of Reports in Molecular Theory, Vol. 1, 1990.
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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D. E. Knuth, Axioms and Hulls, Lect. Notes Comp. Sci., Vol. 606, Springer-Verlag, Berlin, Heidelberg, 1992, p.35, entry C_n.
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CROSSREFS
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Cf. A006245. See A006247 for abstract order types when mirror-symmetric copies are identified.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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