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  2. Figurate number - Wikipedia

    en.wikipedia.org/wiki/Figurate_number

    a number represented as a discrete r-dimensional regular geometric pattern of r-dimensional balls such as a polygonal number (for r = 2) or a polyhedral number (for r = 3). a member of the subset of the sets above containing only triangular numbers, pyramidal numbers , and their analogs in other dimensions.

  3. Triangular number - Wikipedia

    en.wikipedia.org/wiki/Triangular_number

    A triangular number or triangle number counts objects arranged in an equilateral triangle. Triangular numbers are a type of figurate number , other examples being square numbers and cube numbers . The n th triangular number is the number of dots in the triangular arrangement with n dots on each side, and is equal to the sum of the n natural ...

  4. Catalan number - Wikipedia

    en.wikipedia.org/wiki/Catalan_number

    The only Catalan numbers C n that are odd are those for which n = 2 k − 1; all others are even. The only prime Catalan numbers are C 2 = 2 and C 3 = 5. [1] More generally, the multiplicity with which a prime p divides C n can be determined by first expressing n + 1 in base p. For p = 2, the multiplicity is the number

  5. List of two-dimensional geometric shapes - Wikipedia

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

    Henagon – 1 side; Digon – 2 sides; Triangle – 3 sides Acute triangle; Equilateral triangle; Heptagonal triangle; Isosceles triangle. Golden Triangle; Obtuse triangle; Rational triangle; Heronian triangle. Pythagorean triangle; Isosceles heronian triangle; Primitive Heronian triangle; Right triangle. 30-60-90 triangle; Isosceles right ...

  6. Centered triangular number - Wikipedia

    en.wikipedia.org/wiki/Centered_triangular_number

    This is also the number of points of a hexagonal lattice with nearest-neighbor coupling whose distance from a given point is less than or equal to . The following image shows the building of the centered triangular numbers by using the associated figures: at each step, the previous triangle (shown in red) is surrounded by a triangular layer of ...

  7. Circle packing in an equilateral triangle - Wikipedia

    en.wikipedia.org/wiki/Circle_packing_in_an...

    Circle packing in an equilateral triangle is a packing problem in discrete mathematics where the objective is to pack n unit circles into the smallest possible equilateral triangle. Optimal solutions are known for n < 13 and for any triangular number of circles, and conjectures are available for n < 28. [1] [2] [3]

  8. Tetrahedral number - Wikipedia

    en.wikipedia.org/wiki/Tetrahedral_number

    Te 12 = 364 is the total number of gifts "my true love sent to me" during the course of all 12 verses of the carol, "The Twelve Days of Christmas". [3] The cumulative total number of gifts after each verse is also Te n for verse n. The number of possible KeyForge three-house combinations is also a tetrahedral number, Te n−2 where n is the ...

  9. Triangle - Wikipedia

    en.wikipedia.org/wiki/Triangle

    A triangle is a figure consisting of three line segments, each of whose endpoints are connected. [1] This forms a polygon with three sides and three angles. The terminology for categorizing triangles is more than two thousand years old, having been defined in Book One of Euclid's Elements. [2]