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.
%I A048872 #29 Apr 16 2025 09:39:37 %S A048872 1,2,4,17,143,4890,460779 %N A048872 Number of non-isomorphic arrangements of n lines in the real projective plane such that the lines do not all pass through a common point. %D A048872 J. E. Goodman and J. O'Rourke, editors, Handbook of Discrete and Computational Geometry, CRC Press, 1997, p. 102. %D A048872 B. Grünbaum, Arrangements and Spreads. American Mathematical Society, Providence, RI, 1972, p. 4. %H A048872 Stefan Felsner and Jacob E. Goodman, <a href="https://www.csun.edu/~ctoth/Handbook/chap5.pdf">Pseudoline Arrangements</a>, Chapter 5 of Handbook of Discrete and Computational Geometry, CRC Press, 2017, see Table 5.6.1. [Specific reference for this sequence] - _N. J. A. Sloane_, Nov 14 2023 %H A048872 Jacob E. Goodman, Joseph O'Rourke, and Csaba D. Tóth, editors, <a href="https://www.csun.edu/~ctoth/Handbook/HDCG3.html">Handbook of Discrete and Computational Geometry</a>, CRC Press, 2017, see Table 5.6.1. [General reference for 2017 edition of the Handbook] %H A048872 N. J. A. Sloane, <a href="/A048872/a048872.pdf">Illustration of a(3) - a(6)</a> [based on Fig. 2.1 of Grünbaum, 1972] %Y A048872 See A132346 for the sequence when we include the arrangement where the lines do pass through a common point, which is 1 greater than this. %Y A048872 Cf. A003036, A048873, A090338, A090339, A241600, A250001, A018242, A063800 (arrangements of pseudolines). %K A048872 nonn,nice,more %O A048872 3,2 %A A048872 _N. J. A. Sloane_ %E A048872 a(7)-a(9) from Handbook of Discrete and Computational Geometry, 2017, by _Andrey Zabolotskiy_, Oct 09 2017