An N-cluster is a point lattice configuration in which the distance between every pair of points is an integer, no three points are collinear, and no four points are concyclic. An example is the 6-cluster (0, 0), (132, -720), (546, -272), (960, -720), (1155, 540), (546, 1120). Call the radius of the smallest circle centered at one of the points of an N-cluster which contains all the points in the N-cluster the extent. Noll and Bell found 91 nonequivalent prime 6-clusters of extent less than 20937, but found no 7-clusters.

collinear | concyclic | no-three-in-a-line-problem | point lattice | rational distance problem