The curvature (or bend) of a circle of radius
The Descartes circle theorem  states that if four mutually tangent circles have curvatures
If the centers of the circles are
in the complex plane, then
In this Demonstration, the four circles have integer curvatures. The outer circle with center at the origin encloses the other three and has negative curvature, and the other three circles have positive curvatures. At each level, new tangent circles are inscribed into curvilinear triangles tangent to the outer circle; new circles are only added at the edge.
Consider the three largest interior circles for example 42. Their centers have coordinates
and their curvatures are
. The outer circle has curvature
and a piece of data called the global denominator is equal to 5. For each circle, multiplying its center coordinates by the product of its curvature, the outer curvature and the global denominator gives integer values; for the three circles in example 42, the results are
Any subsequently generated edge circle has the same property: the coordinates of the product of the center, curvature, outer curvature and global denominator are integers. The author does not know if this behavior always occurs.
The global denominator seems to always be from the integer sequence 1, 5, 13, 17, 25, 29, 37, ..., the solutions
positive . The author does not know if this behavior always occurs.
Modulus 12, only 4 curvature moduli can occur within an integer curvature circle packing. Circles with a similar modulus get the same color.