OFFSET
1,2
COMMENTS
Partial sums of number of equilateral triangles whose vertices (whether connected by lines or not) lie at intersection points resulting from drawing lines connecting every pair of vertices of a regular 3n-gon (and extending beyond the polygon).
FORMULA
a(n) = Sum_{i=1..n} A036403(i).
EXAMPLE
a(4) = 1 + 126 + 3927 + 33156 = 37210 = 2 * 5 * 61^2.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jonathan Vos Post, Apr 15 2010
STATUS
approved