| bgcolor=#e7dcc3 colspan=2 | 11-cell | |
|---|---|---|
| bgcolor=#ffffff align=center colspan=2 | The 11 hemi-icosahedra with vertices labeled by indices 0..9,t. Faces are colored by the cell it connects to, defined by the small colored boxes. | |
| Type | Abstract regular 4-polytope | |
| Cells | 11 hemi-icosahedron | |
| Faces | 55 | |
| Edges | 55 | |
| Vertices | 11 | |
| Vertex figure | hemi-dodecahedron | |
| Schläfli symbol | \{\{3,5\}5,\{5,3\}5\} | |
| Symmetry group | order 660 Abstract L2(11) | |
| Dual | self-dual | |
| Properties | Regular |
It has symmetry order 660, computed as the product of the number of cells (11) and the symmetry of each cell (60). The symmetry structure is the abstract group projective special linear group of the 2-dimensional vector space over the finite field with 11 elements L2(11).
It was discovered in 1977 by Branko Grünbaum, who constructed it by pasting hemi-icosahedra together, three at each edge, until the shape closed up. It was independently discovered by H. S. M. Coxeter in 1984, who studied its structure and symmetry in greater depth.
Orthographic projection of 10-simplex with 11 vertices, 55 edges.
The abstract 11-cell contains the same number of vertices and edges as the 10-dimensional 10-simplex, and contains 1/3 of its 165 faces. Thus it can be drawn as a regular figure in 10-space, although then its hemi-icosahedral cells are skew; that is, each cell is not contained within a flat 3-dimensional subspace.