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A006246 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)
3
1, 1, 1, 2, 3, 20, 242, 6405, 316835, 28627261, 4686329954 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
COMMENTS
Previous name was: Number of primitive sorting networks on n elements.
REFERENCES
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).
LINKS
D. E. Knuth, Axioms and Hulls, Lect. Notes Comp. Sci., Vol. 606, Springer-Verlag, Berlin, Heidelberg, 1992, p.35, entry C_n.
CROSSREFS
Cf. A006245. See A006247 for abstract order types when mirror-symmetric copies are identified.
Sequence in context: A353921 A361028 A177946 * A349600 A110372 A292866
KEYWORD
nonn
AUTHOR
EXTENSIONS
Definition corrected by Günter Rote, Dec 02 2021
STATUS
approved

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Last modified March 18 22:56 EDT 2024. Contains 370952 sequences. (Running on oeis4.)