A243144 - OEIS

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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

(list; graph; refs; listen; history; text; internal format)

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