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  2. Triangular number - Wikipedia

    en.wikipedia.org/wiki/Triangular_number

    with the sum being the square of the difference between the two (and thus the difference of the two being the square root of the sum): + = (+) + (() + ()) = (+) + = = (). This property, colloquially known as the theorem of Theon of Smyrna , [ 9 ] is visually demonstrated in the following sum, which represents T 4 + T 5 = 5 2 {\displaystyle T_{4 ...

  3. List of sums of reciprocals - Wikipedia

    en.wikipedia.org/wiki/List_of_sums_of_reciprocals

    The harmonic mean of a set of positive integers is the number of numbers times the reciprocal of the sum of their reciprocals. The optic equation requires the sum of the reciprocals of two positive integers a and b to equal the reciprocal of a third positive integer c. All solutions are given by a = mn + m 2, b = mn + n 2, c = mn.

  4. Polite number - Wikipedia

    en.wikipedia.org/wiki/Polite_number

    In number theory, a polite number is a positive integer that can be written as the sum of two or more consecutive positive integers. A positive integer which is not polite is called impolite . [ 1 ] [ 2 ] The impolite numbers are exactly the powers of two , and the polite numbers are the natural numbers that are not powers of two.

  5. Squared triangular number - Wikipedia

    en.wikipedia.org/wiki/Squared_triangular_number

    The sum of the i th row is i times a triangular number, from which it follows that the sum of all the rows is the square of a triangular number. Alternatively, one can decompose the table into a sequence of nested gnomons , each consisting of the products in which the larger of the two terms is some fixed value.

  6. Congruum - Wikipedia

    en.wikipedia.org/wiki/Congruum

    The two right triangles with leg and hypotenuse (7,13) and (13,17) have equal third sides of length .The square of this side, 120, is a congruum: it is the difference between consecutive values in the arithmetic progression of squares 7 2, 13 2, 17 2.

  7. Sums of powers - Wikipedia

    en.wikipedia.org/wiki/Sums_of_powers

    In mathematics and statistics, sums of powers occur in a number of contexts: . Sums of squares arise in many contexts. For example, in geometry, the Pythagorean theorem involves the sum of two squares; in number theory, there are Legendre's three-square theorem and Jacobi's four-square theorem; and in statistics, the analysis of variance involves summing the squares of quantities.

  8. Arithmetic progression - Wikipedia

    en.wikipedia.org/wiki/Arithmetic_progression

    For instance, the sequence 5, 7, 9, 11, 13, 15, . . . is an arithmetic progression with a common difference of 2. If the initial term of an arithmetic progression is a 1 {\displaystyle a_{1}} and the common difference of successive members is d {\displaystyle d} , then the n {\displaystyle n} -th term of the sequence ( a n {\displaystyle a_{n ...

  9. Pronic number - Wikipedia

    en.wikipedia.org/wiki/Pronic_number

    A pronic number is a number that is the product of two consecutive integers, that is, a number of the form (+). [1] The study of these numbers dates back to Aristotle.They are also called oblong numbers, heteromecic numbers, [2] or rectangular numbers; [3] however, the term "rectangular number" has also been applied to the composite numbers.