# Stephanoid

n-gonal stephanoid | |
---|---|

Rank | 3 |

Type | Noble |

Elements | |

Faces | 2n butterflies |

Edges | 2n+2n |

Vertices | 2n |

Vertex figure | Butterfly |

Measures | |

Volume | |

Central density | 0 |

Related polytopes | |

Dual | n-gonal stephanoid |

Convex hull | n-gonal prism or antiprism |

Abstract & topological properties | |

Flag count | 16n |

Euler characteristic | 0 |

Orientable | Yes |

Genus | 1 |

Properties | |

Flag orbits | 8 |

Convex | No |

Nature | Tame |

The **stephanoids** or **crown polyhedra** are an infinite family of self-intersecting self-dual noble polyhedra, meaning that they are both vertex-transitive and face-transitive. All stephanoids have butterfly faces, which are a type of quadrilateral with a an axis of reflectional symmetry formed by crossing two edges of an isosceles trapezoid. The stephanoids have the same vertices and symmetries of the prisms and antiprisms, and they are all toroidal polyhedra with genus 1.

Each stephanoid has a degree of freedom: there are two types of edges and the edge length ratio may be continually varied without losing symmetry properties. Ignoring this variability, the stephanoids are parameterized by three integers: , the number of sides on the polygonal "bases," and two additional parameters and . It is constructed so the faces have vertices steps apart on one base and steps apart on the other base, where and (those cases are degenerate). This gives distinct -gonal stephanoids, although if , , and share a common factor, the resulting stephanoid is a compound. If is even, the convex hull is a prism, else it is an antiprism.

## In vertex figures[edit | edit source]

Square stephanoids appear as the vertex figures of sirc and girc. Pentagonal (1,3)-stephanoids appear as the vertex figures of sriphi, mriphi, griphi, and graphi. Non-noble variants of pentagonal and hexagonal stephanoids appear as the vertex figures of sidpaxhi, gidpaxhi, and toditdy.