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 A366485 #23 Jul 09 2025 05:03:05 %S A366485 3,9,48,237,684,1962,3630,7617,12654,21114,31170,50280,66687,99342, %T A366485 132756,174567,222495,302553,367158,479226,579057,705432,846477, %U A366485 1055679,1217541,1460205,1715088,2011161,2289753,2729301,3044637,3561606,4037604,4587153,5175597,5865729,6432138,7327737 %N A366485 Place n equally spaced points on each side of an equilateral triangle, and join each of these points by a chord to the 2*n new points on the other two sides: sequence gives number of edges in the resulting planar graph. %C A366485 See A366483 for further information. See A366483 and A366486 for images of the triangle. %F A366485 a(n) = A366483(n) + A366486(n) - 1 (Euler). %Y A366485 Cf. A366483 (vertices), A366484 (interior vertices), A366486 (regions). %Y A366485 If the 3*n points are placed "in general position" instead of uniformly, we get sequences A366478, A365929, A366932, A367015. %Y A366485 If the 3*n points are placed uniformly and we also draw chords from the three corner points of the triangle to these 3*n points, we get A274585, A092866, A274586, A092867. %K A366485 nonn %O A366485 0,1 %A A366485 _Scott R. Shannon_ and _N. J. A. Sloane_, Nov 09 2023