A243144 Number of inequivalent (mod D_3) ways to place 5 points on a triangular grid of side n so that they are not vertices of an equilateral triangle of any orientation.
0, 7, 204, 1891, 10846, 46068, 159830, 477033, 1268614, 3075291, 6911894, 14580293, 29145928, 55620816, 101945063, 180327134, 309087474
Offset: 3
Formula
a(n) = (n^10 + 5*n^9 - 30*n^8 - 150*n^7)/23040 + O(n^6).