%I #21 Nov 12 2023 00:07:26
%S 3,9,48,237,684,1962,3630,7617,12654,21114,31170,50280,66687,99342,
%T 132756,174567,222495,302553,367158,479226,579057,705432,846477,
%U 1055679,1217541,1460205,1715088,2011161,2289753,2729301,3044637,3561606,4037604,4587153,5175597,5865729,6432138,7327737
%N 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 See A366483 for further information. See A366483 and A366486 for images of the triangle.
%F a(n) = A366483(n) + A366486(n) - 1 (Euler).
%Y Cf. A366483 (vertices), A366484 (interior vertices), A366486 (regions).
%Y If the 3*n points are placed "in general position" instead of uniformly, we get sequences A366478, A365929, A366932, A367015.
%Y 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 nonn
%O 0,1
%A _Scott R. Shannon_ and _N. J. A. Sloane_, Nov 09 2023.