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, ), (546, ), (960, ), (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 (1989) found 91 nonequivalent prime 6-clusters of extent less than 20937, but found no 7-clusters.
Kreisel and Kurz (2006) subsequently found the 7-cluster given by multiplying the coordinates of the points , , , , , , by , illustrated above.