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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

    1 Solution as a Pell equation. ... a square triangular number ... In 1778 Leonhard Euler determined the explicit formula [1] [2]: 12–13 ...

  4. Solution of triangles - Wikipedia

    en.wikipedia.org/wiki/Solution_of_triangles

    If D > 1, no such triangle exists because the side b does not reach line BC. For the same reason a solution does not exist if the angle β ≥ 90° and b ≤ c. If D = 1, a unique solution exists: γ = 90°, i.e., the triangle is right-angled. If D < 1 two alternatives are possible. If b ≥ c, then β ≥ γ (the larger side corresponds to a ...

  5. Cannonball problem - Wikipedia

    en.wikipedia.org/wiki/Cannonball_problem

    The only numbers that are simultaneously triangular and square pyramidal are 1, 55, 91, and 208335. [ 7 ] [ 8 ] There are no numbers (other than the trivial solution 1) that are both tetrahedral and square pyramidal.

  6. 1 + 2 + 3 + 4 + ⋯ - ⋯ - Wikipedia

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

    One can then prove that this smoothed sum is asymptotic to ⁠− + 1 / 12 ⁠ + CN 2, where C is a constant that depends on f. The constant term of the asymptotic expansion does not depend on f: it is necessarily the same value given by analytic continuation, ⁠− + 1 / 12 ⁠. [1]

  7. Polygonal number - Wikipedia

    en.wikipedia.org/wiki/Polygonal_number

    A computer search for pentagonal square triangular numbers has yielded only the trivial value of 1, though a proof that there are no other such numbers has yet to be found. [ 5 ] The number 1225 is hecatonicositetragonal ( s = 124 ), hexacontagonal ( s = 60 ), icosienneagonal ( s = 29 ), hexagonal, square, and triangular.

  8. 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. [1]

  9. Ramanujan–Nagell equation - Wikipedia

    en.wikipedia.org/wiki/Ramanujan–Nagell_equation

    The equation is = and solutions in natural numbers n and x exist just when n = 3, 4, 5, 7 and 15 (sequence A060728 in the OEIS).. This was conjectured in 1913 by Indian mathematician Srinivasa Ramanujan, proposed independently in 1943 by the Norwegian mathematician Wilhelm Ljunggren, and proved in 1948 by the Norwegian mathematician Trygve Nagell.