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  2. 28 (number) - Wikipedia

    en.wikipedia.org/wiki/28_(number)

    The number 28 depicted as 28 balls arranged in a triangular pattern with the number of layers of 7 28 as the sum of four nonzero squares. Twenty-eight is a composite number and the second perfect number as it is the sum of its proper divisors: 1 + 2 + 4 + 7 + 14 = 28 {\displaystyle 1+2+4+7+14=28} .

  3. Perfect number - Wikipedia

    en.wikipedia.org/wiki/Perfect_number

    In number theory, a perfect number is a positive integer that is equal to the sum of its positive proper divisors, that is, divisors excluding the number itself. [1] For instance, 6 has proper divisors 1, 2 and 3, and 1 + 2 + 3 = 6, so 6 is a perfect number. The next perfect number is 28, since 1 + 2 + 4 + 7 + 14 = 28.

  4. List of types of numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_types_of_numbers

    Prime number: A positive integer with exactly two positive divisors: itself and 1. The primes form an infinite sequence 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, ... Composite number: A positive integer that can be factored into a product of smaller positive integers. Every integer greater than one is either prime or composite.

  5. Table of divisors - Wikipedia

    en.wikipedia.org/wiki/Table_of_divisors

    a highly composite number has a number of positive divisors that is greater than any lesser number; ... 28, 32, 56, 64, 112, 128, 224, 448, 896 16 2040 1144

  6. Positive real numbers - Wikipedia

    en.wikipedia.org/wiki/Positive_real_numbers

    Including 0, the set has a semiring structure (0 being the additive identity), known as the probability semiring; taking logarithms (with a choice of base giving a logarithmic unit) gives an isomorphism with the log semiring (with 0 corresponding to ), and its units (the finite numbers, excluding ) correspond to the positive real numbers.

  7. Polite number - Wikipedia

    en.wikipedia.org/wiki/Polite_number

    The politeness of a positive number is defined as the number of ways it can be expressed as the sum of consecutive integers. ... the perfect number 28 = 2 3 − 1 ...

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    mail.aol.com/?rp=webmail-std/en-us/basic

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  9. List of mathematical constants - Wikipedia

    en.wikipedia.org/wiki/List_of_mathematical_constants

    Positive root of = 1800 to 1600 BCE [5] ... Soldner constant [28] ... Smallest positive real number A such that ...