OFFSET
1,4
COMMENTS
The Mathoverflow link has an image from page 200 of Brass reference.
REFERENCES
P. Brass, W. O. J. Moser and J. Pach, Research Problems in Discrete Geometry, Springer (2005), p. 200.
LINKS
P. Erdős and P. Fishburn, Maximum planar sets that determine k distances, Discrete Math. 160 (1996), 115-125.
L. Guth and N. H. Katz, On the Erdős distinct distance problem in the plane, arXiv:1011.4105 [math.CO], 2010-2011.
R. Mansuy, Le problème des distances d'Erdős, Mathematik Park, Institut Henri Poincaré, Paris, 2013.
Mathoverflow, Erdos distance problem n=12
K. Schade, Softwarepraktikum, Sommersemester 2007
EXAMPLE
a(4) = a(5) = 2 from the 2 distinct distances between vertices of a square and a regular pentagon.
CROSSREFS
KEYWORD
nonn,hard,more,nice
AUTHOR
Michael Somos, Feb 25 2011
STATUS
approved