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Count the number of regular and star polygons in a circle

Source: Romanian IMO Team Selection Test TST 1988, problem 3

October 1, 2005
geometrygeometric transformationrotationcombinatorics proposedcombinatorics

Problem Statement

Consider all regular convex and star polygons inscribed in a given circle and having nn sides. We call two such polygons to be equivalent if it is possible to obtain one from the other using a rotation about the center of the circle. How many classes of such polygons exist? Mircea Becheanu