A243210 Number of inequivalent (mod D_3) ways to place 5 points on a triangular grid of side n so that no three of them are vertices of an equilateral triangle with sides parallel to the grid.

0, 11, 266, 2344, 12907, 53307, 180876, 530654, 1391647, 3335627, 7426885, 15544434, 30867669, 58574800, 106838511, 188190111, 321383808, 533857914

Offset

3,2

Links

Table of n, a(n) for n=3..20.

Formula

a(n) = (n^10 + 5*n^9 - 10*n^8 - 195*n^7)/23040 + O(n^6)

Crossrefs

Cf. A243207, A243214, A001399, A227327, A243208, A243209.

Sequence in context: A356212 A100841 A003389 * A232695 A027019 A255955

Adjacent sequences: A243207 A243208 A243209 * A243211 A243212 A243213

Keyword

nonn,more

Author

Heinrich Ludwig, Jun 10 2014

Status

approved