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A350547 Maximum size of a set of points taken from a hexagonal section of a hexagonal grid with side length n such that no three selected points form an equilateral triangle. 0
1, 4, 9, 15, 22, 28, 36 (list; graph; refs; listen; history; text; internal format)
The hexagon with side length n has n+1 points along each edge and contains a total of A003215(n) points.
The following lower bounds are known:
a(7) >= 44;
a(8) >= 52;
a(9) >= 60.
All currently known values and lower bounds can be achieved by a configuration with reflective symmetry.
For n = 4 the a(4) = 22 solution, unique up to rotation, is:
o x x o x
x x o o o x
x o o o o x o
o o o o o o x x
x o o o o o o o x
x x o o o o o o
o x o o o o x
x o o o x x
x o x x o
Sequence in context: A066495 A313298 A313299 * A055999 A134227 A022945
Zachary DeStefano, Jan 06 2022

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Last modified December 11 13:02 EST 2023. Contains 367727 sequences. (Running on oeis4.)