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A271907 Size of the largest subset S of the points of an n X n square grid such that no three of the points of S form an isosceles triangle. 3
1, 2, 4, 6, 8, 10, 12, 14, 16, 18 (list; graph; refs; listen; history; text; internal format)



S must not contain 3 points A,B,C such that |AB| = |BC|.

For example, this configuration is forbidden:

   O O O B

   O O O O

   A O O O

   O C O O

It appears that this is simply a(n) = 2n-2 for n>1, and if so this entry may be replaced by a comment in A271914 and A271906, and this A-number recycled.


Table of n, a(n) for n=1..10.


Illustration for a(3) = 4:

   O X X

   X O O

   X O O

Illustration for a(8) = 14:

   O X X X X X O X

   X O O O O O O X

   X O O O O O O O

   X O O O O O O O

   X O O O O O O O

   X O O O O O O O

   O O O O O O O O

   X X O O O O O O


Cf. A271906, A227133.

Main diagonal of A271914.

Sequence in context: A319747 A055958 A241142 * A069816 A088116 A100817

Adjacent sequences:  A271904 A271905 A271906 * A271908 A271909 A271910




Giovanni Resta and N. J. A. Sloane, Apr 22 2016



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Last modified July 29 17:41 EDT 2021. Contains 346346 sequences. (Running on oeis4.)