cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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).

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%I A006246 M0920 #46 Mar 18 2025 16:24:51
%S A006246 1,1,1,2,3,20,242,6405,316835,28627261,4686329954,1382939012729,
%T A006246 732955581630129
%N 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).
%C A006246 Previous name was: Number of primitive sorting networks on n elements.
%D A006246 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.
%D A006246 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A006246 D. E. Knuth, <a href="https://doi.org/10.1007/3-540-55611-7">Axioms and Hulls</a>, Lect. Notes Comp. Sci., Vol. 606, Springer-Verlag, Berlin, Heidelberg, 1992, p.35, entry C_n.
%H A006246 Günter Rote, <a href="https://arxiv.org/abs/2503.02336">NumPSLA — An experimental research tool for pseudoline arrangements and order types</a>, arXiv:2503.02336 [math.CO], 2025. See Table 5 on p. 18:17, last column.
%H A006246 <a href="/index/So#sorting">Index entries for sequences related to sorting</a>
%Y A006246 Cf. A006245. See A006247 for abstract order types when mirror-symmetric copies are identified.
%K A006246 nonn,more
%O A006246 1,4
%A A006246 _N. J. A. Sloane_
%E A006246 Definition corrected by _Günter Rote_, Dec 02 2021
%E A006246 a(12) and a(13) from _Günter Rote_, Mar 04 2025