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).

1, 1, 1, 2, 3, 20, 242, 6405, 316835, 28627261, 4686329954, 1382939012729, 732955581630129

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• more

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.
• Günter Rote, NumPSLA — An experimental research tool for pseudoline arrangements and order types, arXiv:2503.02336 [math.CO], 2025. See Table 5 on p. 18:17, last column.
• Index entries for sequences related to sorting

Crossrefs

Cf. A006245. See A006247 for abstract order types when mirror-symmetric copies are identified.

Extensions

Definition corrected by Günter Rote, Dec 02 2021

a(12) and a(13) from Günter Rote, Mar 04 2025