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  2. Tetrahedron - Wikipedia

    en.wikipedia.org/wiki/Tetrahedron

    The tetrahedron is one kind of pyramid, which is a polyhedron with a flat polygon base and triangular faces connecting the base to a common point. In the case of a tetrahedron, the base is a triangle (any of the four faces can be considered the base), so a tetrahedron is also known as a "triangular pyramid".

  3. Pyramid (geometry) - Wikipedia

    en.wikipedia.org/wiki/Pyramid_(geometry)

    [17] [18] A tetrahedron or triangular pyramid is an example that has four equilateral triangles, with all edges equal in length, and one of them is considered as the base. Because the faces are regular, it is an example of a Platonic solid and deltahedra, and it has tetrahedral symmetry. [19] [20] A pyramid with the base as circle is known as ...

  4. Tetrahedral number - Wikipedia

    en.wikipedia.org/wiki/Tetrahedral_number

    A pyramid with side length 5 contains 35 spheres. Each layer represents one of the first five triangular numbers. A tetrahedral number, or triangular pyramidal number, is a figurate number that represents a pyramid with a triangular base and three sides, called a tetrahedron.

  5. Pyramid - Wikipedia

    en.wikipedia.org/wiki/Pyramid

    Pyramid of Khafre, Egypt, built c. 2600 BC. A pyramid (from Ancient Greek πυραμίς (puramís) 'pyramid') [1] [2] is a structure whose visible surfaces are triangular in broad outline and converge toward the top, making the appearance roughly a pyramid in the geometric sense.

  6. Truncated triangular pyramid number - Wikipedia

    en.wikipedia.org/wiki/Truncated_Triangular...

    A pyramid with side length 5 contains 35 spheres. Each layer represents one of the first five triangular numbers. A truncated triangular pyramid number [1] is found by removing some smaller tetrahedral number (or triangular pyramidal number) from each of the vertices of a bigger tetrahedral number.

  7. Pyramidal number - Wikipedia

    en.wikipedia.org/wiki/Pyramidal_number

    A pyramidal number is the number of points in a pyramid with a polygonal base and triangular sides. [1] The term often refers to square pyramidal numbers , which have a square base with four sides, but it can also refer to a pyramid with any number of sides. [ 2 ]

  8. Conway polyhedron notation - Wikipedia

    en.wikipedia.org/wiki/Conway_polyhedron_notation

    Triangular pyramid: Y 3 (A tetrahedron is a special pyramid) T = Y 3; O = aT (ambo tetrahedron) C = jT (join tetrahedron) I = sT (snub tetrahedron) D = gT (gyro tetrahedron) Triangular antiprism: A 3 (An octahedron is a special antiprism) O = A 3; C = dA 3; Square prism: P 4 (A cube is a special prism) C = P 4; Pentagonal antiprism: A 5. I = k ...

  9. 5-cell - Wikipedia

    en.wikipedia.org/wiki/5-cell

    The tetrahedral pyramid is a special case of a 5-cell, a polyhedral pyramid, constructed as a regular tetrahedron base in a 3-space hyperplane, and an apex point above the hyperplane. The four sides of the pyramid are made of triangular pyramid cells. Many uniform 5-polytopes have tetrahedral pyramid vertex figures with Schläfli symbols ( )∨ ...