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

3,2

Links

Table of n, a(n) for n=3..19.

Formula

a(n) = (n^10 + 5*n^9 - 30*n^8 - 150*n^7)/23040 + O(n^6).

Crossrefs

Cf. A243141, A240442, A001399, A227327, A243142, A243143.

Sequence in context: A177813 A292338 A216456 * A234619 A308614 A178022

Adjacent sequences: A243141 A243142 A243143 * A243145 A243146 A243147

Keyword

nonn,more

Author

Heinrich Ludwig, May 31 2014

Status

approved