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  2. Triangular number - Wikipedia

    en.wikipedia.org/wiki/Triangular_number

    The final digit of a triangular number is 0, 1, 3, 5, 6, or 8, and thus such numbers never end in 2, 4, 7, or 9. A final 3 must be preceded by a 0 or 5; a final 8 must be preceded by a 2 or 7. In base 10, the digital root of a nonzero triangular number is always 1, 3, 6, or 9. Hence, every triangular number is either divisible by three or has a ...

  3. List of types of numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_types_of_numbers

    Polygonal numbers: These are numbers that can be represented as dots that are arranged in the shape of a regular polygon, including Triangular numbers, Square numbers, Pentagonal numbers, Hexagonal numbers, Heptagonal numbers, Octagonal numbers, Nonagonal numbers, Decagonal numbers, Hendecagonal numbers, and Dodecagonal numbers.

  4. Centered triangular number - Wikipedia

    en.wikipedia.org/wiki/Centered_triangular_number

    Each centered triangular number has a remainder of 1 when divided by 3, and the quotient (if positive) is the previous regular triangular number. Each centered triangular number from 10 onwards is the sum of three consecutive regular triangular numbers. For n > 2, the sum of the first n centered triangular numbers is the magic constant for an n ...

  5. Square triangular number - Wikipedia

    en.wikipedia.org/wiki/Square_triangular_number

    Consequently, a square number is also triangular if and only if + is square, that is, there are numbers and such that =. This is an instance of the Pell equation x 2 − n y 2 = 1 {\displaystyle x^{2}-ny^{2}=1} with n = 8 {\displaystyle n=8} .

  6. Tetrahedral number - Wikipedia

    en.wikipedia.org/wiki/Tetrahedral_number

    Te n is the sum of all products p × q where (p, q) are ordered pairs and p + q = n + 1; Te n is the number of (n + 2)-bit numbers that contain two runs of 1's in their binary expansion. The largest tetrahedral number of the form + + for some integers and is 8436.

  7. Doubly triangular number - Wikipedia

    en.wikipedia.org/wiki/Doubly_triangular_number

    In mathematics, the doubly triangular numbers are the numbers that appear within the sequence of triangular numbers, in positions that are also triangular numbers. That is, if T n = n ( n + 1 ) / 2 {\displaystyle T_{n}=n(n+1)/2} denotes the n {\displaystyle n} th triangular number, then the doubly triangular numbers are the numbers of the form ...

  8. 1 + 2 + 3 + 4 + ⋯ - ⋯ - Wikipedia

    en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E...

    The first six triangular numbers. The partial sums of the series 1 + 2 + 3 + 4 + 5 + 6 + ⋯ are 1, 3, 6, 10, 15, etc.The nth partial sum is given by a simple formula

  9. Category:Triangles of numbers - Wikipedia

    en.wikipedia.org/wiki/Category:Triangles_of_numbers

    This page was last edited on 20 February 2023, at 19:48 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.