Deltahedron
A semiregular Polyhedron whose faces are all Equilateral Triangles. There are aninfinite number of deltahedra, but only eight convex ones (Freudenthal and van der Waerden 1947). They have 4, 6, 8, 10, 12,14, 16, and 20 faces. These are summarized in the table below, and illustrated in the following figures.
 | Name |
| 4 | Tetrahedron |
| 6 | Triangular Dipyramid |
| 8 | Octahedron |
| 10 | Pentagonal Dipyramid |
| 12 | Snub Disphenoid |
| 14 | Triaugmented Triangular Prism |
| 16 | Gyroelongated Square Dipyramid |
| 20 | Icosahedron |
The Stella Octangula is a concave deltahedron with 24 sides:
Another with 60 faces is a ``caved in'' Dodecahedron which is Icosahedron Stellation 
.
Cundy (1952) identifies 17 concave deltahedra with two kinds of Vertices.
See also Gyroelongated Square Dipyramid, Icosahedron, Octahedron, Pentagonal Dipyramid, SnubDisphenoid Tetrahedron, Triangular Dipyramid, Triaugmented Triangular Prism
References
Cundy, H. M. ``Deltahedra.'' Math. Gaz. 36, 263-266, 1952. Freudenthal, H. and van der Waerden, B. L. ``On an Assertion of Euclid.'' Simon Stevin 25, 115-121, 1947. Gardner, M. Fractal Music, Hypercards, and More: Mathematical Recreations from Scientific American Magazine. New York: W. H. Freeman, pp. 40, 53, and 58-60, 1992. Pugh, A. Polyhedra: A Visual Approach. Berkeley, CA: University of California Press, pp. 35-36, 1976.
- Weierstraß Elliptic Function
- Weierstraß-Erdman Corner Condition
- Weierstraß Extreme Value Theorem
- Weierstraß Form
- Weierstraß Function
- Weierstraß Intermediate Value Theorem
- Weierstraß Point
- Weierstraß Product Inequality
- Weierstraß's Gap Theorem
- Weierstraß Sigma Function
- Weierstraß's Polynomial Theorem
- Weierstraß's Theorem
- Weierstraß Zeta Function
- Weighings
- Weight
- Weighted Tree
- Weight Function
- Weighting Function
- Weingarten Equations
- Weingarten Map
- Weird Number
- Welch Apodization Function
- Well-Defined
- Well-Ordered Set
- Well-Ordering Principle