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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. 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} .

  4. 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.

  5. Squared triangular number - Wikipedia

    en.wikipedia.org/wiki/Squared_triangular_number

    A square whose side length is a triangular number can be partitioned into squares and half-squares whose areas add to cubes. From Gulley (2010).The n th coloured region shows n squares of dimension n by n (the rectangle is 1 evenly divided square), hence the area of the n th region is n times n × n.

  6. 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 ...

  7. Floyd's triangle - Wikipedia

    en.wikipedia.org/wiki/Floyd's_triangle

    The numbers along the left edge of the triangle are the lazy caterer's sequence and the numbers along the right edge are the triangular numbers. The nth row sums to n(n 2 + 1)/2, the constant of an n × n magic square (sequence A006003 in the OEIS). Summing up the row sums in Floyd's triangle reveals the doubly triangular numbers, triangular ...

  8. Doubly triangular number - Wikipedia

    en.wikipedia.org/wiki/Doubly_triangular_number

    The th doubly triangular number is given by the quartic formula [2] = (+) (+ +). The sums of row sums of Floyd's triangle give the doubly triangular numbers. Another way of expressing this fact is that the sum of all of the numbers in the first n {\displaystyle n} rows of Floyd's triangle is the n {\displaystyle n} th doubly triangular number.

  9. Truncated triangular pyramid number - Wikipedia

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

    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. The number to be removed may be same or different from each of the vertices. [2]