The [url=https://en.wikipedia.org/wiki/Szilassi_polyhedron]Szilassi polyhedron[/url] has seven hexagonal faces. Topologically it is a torus, that is, if it were smoothed out, it might be a "doughnut".[br]It was discovered in 1977 by Hungarian mathematician Lajos Szilassi with support of computer based calculations. This GeoGebra applet has been created by [url=https://tube.geogebra.org/gengiskunk#]Paolo Eustacchio[/url].[br]The Szilassi polyhedron has 14 vertexes, 21 edges, and a hole. Like the tetrahedron, it has the remarkable property that each of its faces touches all the other faces. As a result, it requires seven colours to colour each adjacent face, providing the lower bound for the [url=https://en.wikipedia.org/wiki/Seven_colour_theorem]seven colour theorem[/url] on toruses.[br]A stainless steel sculpture model of the polyhedron can be found in [url=http://www.beaumont-de-lomagne.fr/fr/pierre-fermat/le-polyedre-de-szilassi.html]Beaumont de Lomagne[/url], France, in Pierre de Fermat's house, since 2002.