Uniform 2 k1 polytope
In geometry, 2k1 polytope is a uniform polytope in n dimensions (n = k+4) constructed from the En Coxeter group. The family was named by their Coxeter symbol as 2k1 by its bifurcating Coxeter-Dynkin diagram, with a single ring on the end of the 2-node sequence. It can be named by an extended Schläfli symbol {3,3,3k,1}.
Family members
    
The family starts uniquely as 6-polytopes, but can be extended backwards to include the 5-orthoplex (pentacross) in 5-dimensions, and the 4-simplex (5-cell) in 4-dimensions.
Each polytope is constructed from (n-1)-simplex and 2k-1,1 (n-1)-polytope facets, each has a vertex figure as an (n-1)-demicube, {31,n-2,1}.
The sequence ends with k=6 (n=10), as an infinite hyperbolic tessellation of 9-space.
The complete family of 2k1 polytope polytopes are:
- 5-cell: 201, (5 tetrahedra cells)
 - Pentacross: 211, (32 5-cell (201) facets)
 - 221, (72 5-simplex and 27 5-orthoplex (211) facets)
 - 231, (576 6-simplex and 56 221 facets)
 - 241, (17280 7-simplex and 240 231 facets)
 - 251, tessellates Euclidean 8-space (∞ 8-simplex and ∞ 241 facets)
 - 261, tessellates hyperbolic 9-space (∞ 9-simplex and ∞ 251 facets)
 
Elements
    
| n | 2k1 | Petrie polygon projection  | 
Name Coxeter-Dynkin diagram  | 
Facets | Elements | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2k-1,1 polytope | (n-1)-simplex | Vertices | Edges | Faces | Cells | 4-faces | 5-faces | 6-faces | 7-faces | ||||
| 4 | 201 | ![]()  | 
5-cell {32,0,1}  | 
-- | 5 {33}  | 
5 | 10 | 10 | 
5 | ||||
| 5 | 211 | ![]()  | 
pentacross {32,1,1}  | 
16 {32,0,1}  | 
16 {34}  | 
10 | 40 | 80 | 
80 | 
32 | 
|||
| 6 | 221 | ![]()  | 
2 21 polytope {32,2,1}  | 
27 {32,1,1}  | 
72 {35}  | 
27 | 216 | 720 | 
1080 | 
648 | 
99 | 
||
| 7 | 231 | ![]()  | 
2 31 polytope {32,3,1}  | 
56 {32,2,1}  | 
576 {36}  | 
126 | 2016 | 10080 | 
20160 | 
16128 | 
4788 | 
632 | 
|
| 8 | 241 | ![]()  | 
2 41 polytope {32,4,1}  | 
240 {32,3,1}  | 
17280 {37}  | 
2160 | 69120 | 483840 | 
1209600 | 
1209600 | 
544320 | 
144960 | 
17520 | 
| 9 | 251 | 2 51 honeycomb (8-space tessellation) {32,5,1}  | 
∞ {32,4,1}  | 
∞ {38}  | 
∞ | ||||||||
| 10 | 261 | 2 61 honeycomb (9-space tessellation) {32,6,1}  | 
∞ {32,5,1}  | 
∞ {39}  | 
∞ | ||||||||
See also
    
- k21 polytope family
 - 1k2 polytope family
 
References
    
- Alicia Boole Stott Geometrical deduction of semiregular from regular polytopes and space fillings, Verhandelingen of the Koninklijke academy van Wetenschappen width unit Amsterdam, Eerste Sectie 11,1, Amsterdam, 1910
- Stott, A. B. "Geometrical Deduction of Semiregular from Regular Polytopes and Space Fillings." Verhandelingen der Koninklijke Akad. Wetenschappen Amsterdam 11, 3-24, 1910.
 - Alicia Boole Stott, "Geometrical deduction of semiregular from regular polytopes and space fillings," Verhandelingen der Koninklijke Akademie van Wetenschappen te Amsterdam, (eerste sectie), Vol. 11, No. 1, pp. 1–24 plus 3 plates, 1910.
 - Stott, A. B. 1910. "Geometrical Deduction of Semiregular from Regular Polytopes and Space Fillings." Verhandelingen der Koninklijke Akad. Wetenschappen Amsterdam
 
 - Schoute, P. H., Analytical treatment of the polytopes regularly derived from the regular polytopes, Ver. der Koninklijke Akad. van Wetenschappen te Amsterdam (eerstie sectie), vol 11.5, 1913.
 - H. S. M. Coxeter: Regular and Semi-Regular Polytopes, Part I, Mathematische Zeitschrift, Springer, Berlin, 1940
 - N.W. Johnson: The Theory of Uniform Polytopes and Honeycombs, Ph.D. Dissertation, University of Toronto, 1966
 - H.S.M. Coxeter: Regular and Semi-Regular Polytopes, Part II, Mathematische Zeitschrift, Springer, Berlin, 1985
 - H.S.M. Coxeter: Regular and Semi-Regular Polytopes, Part III, Mathematische Zeitschrift, Springer, Berlin, 1988
 
External links
    
| Space | Family | / / | ||||
|---|---|---|---|---|---|---|
| E2 | Uniform tiling | {3[3]} | δ3 | hδ3 | qδ3 | Hexagonal | 
| E3 | Uniform convex honeycomb | {3[4]} | δ4 | hδ4 | qδ4 | |
| E4 | Uniform 4-honeycomb | {3[5]} | δ5 | hδ5 | qδ5 | 24-cell honeycomb | 
| E5 | Uniform 5-honeycomb | {3[6]} | δ6 | hδ6 | qδ6 | |
| E6 | Uniform 6-honeycomb | {3[7]} | δ7 | hδ7 | qδ7 | 222 | 
| E7 | Uniform 7-honeycomb | {3[8]} | δ8 | hδ8 | qδ8 | 133 • 331 | 
| E8 | Uniform 8-honeycomb | {3[9]} | δ9 | hδ9 | qδ9 | 152 • 251 • 521 | 
| E9 | Uniform 9-honeycomb | {3[10]} | δ10 | hδ10 | qδ10 | |
| E10 | Uniform 10-honeycomb | {3[11]} | δ11 | hδ11 | qδ11 | |
| En-1 | Uniform (n-1)-honeycomb | {3[n]} | δn | hδn | qδn | 1k2 • 2k1 • k21 | 




