Starting with the circle tangent to the three semicircles forming the arbelos, construct a chain of tangent circles , all tangent to one of the two small interior circles and to the large exterior one. This chain is called the Pappus chain (left figure).
In a Pappus chain, the distance from the center of the first inscribed circle to the bottom line is twice the circle's radius, from the second circle is four times the radius, and for the th circle is times the radius. Furthermore, the centers of the circles lie on an ellipse (right figure).
If , then the center and radius of the th circle in the Pappus chain are