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  2. Pyramidal number - Wikipedia

    en.wikipedia.org/wiki/Pyramidal_number

    Geometric representation of the square pyramidal number 1 + 4 + 9 + 16 = 30. 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]

  3. Scheme (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Scheme_(mathematics)

    In mathematics, specifically algebraic geometry, a scheme is a structure that enlarges the notion of algebraic variety in several ways, such as taking account of multiplicities (the equations x = 0 and x 2 = 0 define the same algebraic variety but different schemes) and allowing "varieties" defined over any commutative ring (for example, Fermat curves are defined over the integers).

  4. Pyramid (geometry) - Wikipedia

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

    Rarely, a right pyramid is defined to be a pyramid whose base is circumscribed about a circle and the altitude of the pyramid meets the base at the circle's center. [ 17 ] For the pyramid with an n - sided regular base, it has n + 1 vertices, n + 1 faces, and 2 n edges. [ 18 ]

  5. Square pyramidal number - Wikipedia

    en.wikipedia.org/wiki/Square_pyramidal_number

    Geometric representation of the square pyramidal number 1 + 4 + 9 + 16 = 30. In mathematics, a pyramid number, or square pyramidal number, is a natural number that counts the stacked spheres in a pyramid with a square base. The study of these numbers goes back to Archimedes and Fibonacci.

  6. 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.

  7. Pyramid scheme - Wikipedia

    en.wikipedia.org/wiki/Pyramid_scheme

    The pyramid scheme in the picture in contrast is a geometric progression 1 + 2 + 4 + 8 = 15. Many pyramids are more sophisticated than the simple model. These recognize that recruiting a large number of others into a scheme can be difficult, so a seemingly simpler model is used.

  8. List of two-dimensional geometric shapes - Wikipedia

    en.wikipedia.org/wiki/List_of_two-dimensional...

    This is a list of two-dimensional geometric shapes in Euclidean and other geometries. For mathematical objects in more dimensions, see list of mathematical shapes. For a broader scope, see list of shapes.

  9. Figurate number - Wikipedia

    en.wikipedia.org/wiki/Figurate_number

    This gnomonic technique also provides a mathematical proof that the sum of the first n odd numbers is n 2; the figure illustrates 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 = 64 = 8 2. There is a similar gnomon with centered hexagonal numbers adding up to make cubes of each integer number.