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%I #16 Mar 31 2012 10:23:03
%S 1,1,1,8,73,174,22270
%N Minimum diameter of an integral set of n points in the plane, no 3 on a line, no 4 on a circle.
%C An integral set is a set where all distances between points are integers.
%C As of 2011, it is not known if this sequence is finite or even if a(8) exists.
%D H. Harborth, Integral distances in point sets, Butzer, P. L. (ed.) et al., Karl der Grosse und sein Nachwirken. 1200 Jahre Kultur und Wissenschaft in Europa. Band 2: Mathematisches Wissen. Turnhout: Brepols. 213-224 (1998).
%H Tobias Kreisel, Sascha Kurz, <a href="http://www.wm.uni-bayreuth.de/fileadmin/Sascha/Publikationen2/rare.pdf">There are integral heptagons, no three points on a line, no four on a circle</a>, preprint (2006)
%H T. Kreisel and S. Kurz, <a href="http://dx.doi.org/10.1007/s00454-007-9038-6">There are integral heptagons, no three points on a line, no four on a circle</a>, Discrete and Computational Geometry 39 Issue 4 (2008), 786-790, MR2413160
%H J. Solymosi and F. de Zeeuw, <a href="http://dx.doi.org/10.1007/s00454-009-9179-x">On a Question of Erdos and Ulam</a>, Discrete and Computational Geometry Vol. 43 Issue 2 (2010), 393-401.
%Y Cf. A007285, A096872.
%K hard,nonn,more
%O 1,4
%A _Sascha Kurz_, Jul 13 2004
%E a(7) computed in [Kreisel-Kurz].
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