please expand

[Don Reble]

> 1,3,6,9,12,16,21,
> %N A000001 a(n) is the maximum number of points on a n by n square grid such that no 4 points form a rectangle having sides parallel to the sides of the grid.
> %C A000001 a(7) is presented as a puzzle in Mathematical Gems III by Ross Honsberger on page 4.

     It looks like A072567 is missing an initial '1'.
-- 
Don Reble  djr at nk.ca



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