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

3,2

Links

Table of n, a(n) for n=3..18.

Formula

a(n) = (n^10 + 5*n^9 - 30*n^8 - 150*n^7)/3840 + O(n^6).

Crossrefs

Cf. A240439, A240440, A240441.

Sequence in context: A251327 A014936 A227524 * A009729 A078970 A020303

Adjacent sequences: A240439 A240440 A240441 * A240443 A240444 A240445

Keyword

nonn,more

Author

Heinrich Ludwig, Apr 08 2014

Extensions

a(16)-a(18) from Heinrich Ludwig, Apr 25 2014

Status

approved