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 A230503 #13 Oct 22 2013 16:25:02 %S A230503 0,1,5,13,15,29,31,33,35,49,52,53,54,56,57,58,59,60,61,62,63,64,65,66, %T A230503 68,70 %N A230503 Irregular triangle read by rows: possible number of interior intersection points of the diagonals of an n-sided convex polygon. %C A230503 Beginning from number of sides equal to 12 the terms no longer increase between rows. For example, the number of inner diagonal intersection points for the regular 12-gon is fewer than the number of inner diagonal intersection points for regular 11-gon. %C A230503 Obviously there exists a number k_0 such that k_0 is not in the sequence and k is in the sequence for all k > k_0. %H A230503 Vladimir Letsko, <a href="http://www-old.fizmat.vspu.ru/doku.php?id=marathon:problem_102">Mathematical Marathon at vspu, Problem 102</a> (in Russian) %H A230503 Vladimir Letsko <a href="http://www-old.fizmat.vspu.ru/doku.php?id=marathon:illustrations_102_co">Illustration of all cases for number of sides from 3 to 8</a> %H A230503 V. A. Letsko and M. A. Voronina <a href="http://grani.vspu.ru/files/publics/1301378772.pdf">Classification of convex polygons</a>, Grani Poznaniya, 1(11), 2011 (in Russian). %e A230503 The beginning of the irregular triangle is: %e A230503 3| 0 %e A230503 4| 1 %e A230503 5| 5 %e A230503 6| 13, 15 %e A230503 7| 29, 31, 33, 35 %e A230503 8| 49, 52, 53, 54, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 68, 70 %Y A230503 Cf. A006561, A230281, A000332, A230150. %K A230503 tabf,more,nonn %O A230503 3,3 %A A230503 _Vladimir Letsko_, Oct 21 2013