A240442 Number of ways to place 5 points on a triangular grid of side n so that no three of these points are vertices of an equilateral triangle of any orientation.
0, 39, 1194, 11259, 64776, 275805, 957516, 2859768, 7606821, 18444537, 41458599, 87464157, 174846963, 333687378, 611613150, 1081890447
Offset: 3
Formula
a(n) = (n^10 + 5*n^9 - 30*n^8 - 150*n^7)/3840 + O(n^6).
Extensions
a(16)-a(18) from Heinrich Ludwig, Apr 25 2014