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  2. Collatz conjecture - Wikipedia

    en.wikipedia.org/wiki/Collatz_conjecture

    If it can be shown that for all positive integers less than the Collatz sequences reach 1, then this bound would raise to 217 976 794 617 (355 504 839 929 without shortcut). [ 20 ] [ 14 ] In fact, Eliahou (1993) proved that the period p of any non-trivial cycle is of the form p = 301994 a + 17087915 b + 85137581 c {\displaystyle p=301994a ...

  3. Wilson's theorem - Wikipedia

    en.wikipedia.org/wiki/Wilson's_theorem

    Wilson's theorem. In algebra and number theory, Wilson's theorem states that a natural number n > 1 is a prime number if and only if the product of all the positive integers less than n is one less than a multiple of n. That is (using the notations of modular arithmetic), the factorial satisfies. exactly when n is a prime number.

  4. Natural number - Wikipedia

    en.wikipedia.org/wiki/Natural_number

    Starting at 0 or 1 has long been a matter of definition. In 1727, Bernard Le Bovier de Fontenelle wrote that his notions of distance and element led to defining the natural numbers as including or excluding 0. [23] In 1889, Giuseppe Peano used N for the positive integers and started at 1, [24] but he later changed to using N 0 and N 1. [25]

  5. Integer - Wikipedia

    en.wikipedia.org/wiki/Integer

    The integers arranged on a number line. An integer is the number zero , a positive natural number (1, 2, 3, . . .), or the negation of a positive natural number (−1, −2, −3, . . .). [1] The negations or additive inverses of the positive natural numbers are referred to as negative integers. [2]

  6. Divisibility rule - Wikipedia

    en.wikipedia.org/wiki/Divisibility_rule

    Then we apply the algorithm: 1 × 15 − 3 × 75 + 2 × 14 = 182 Because the resulting 182 is less than six digits, we add zero's to the right side until it is six digits. Then we apply our algorithm again: 1 × 18 − 3 × 20 + 2 × 0 = −42 The result −42 is divisible by seven, thus the original number 157514 is divisible by seven. Example 2:

  7. Composite number - Wikipedia

    en.wikipedia.org/wiki/Composite_number

    A composite number is a positive integer that can be formed by multiplying two smaller positive integers. Equivalently, it is a positive integer that has at least one divisor other than 1 and itself. [1][2] Every positive integer is composite, prime, or the unit 1, so the composite numbers are exactly the numbers that are not prime and not a ...

  8. Deficient number - Wikipedia

    en.wikipedia.org/wiki/Deficient_number

    Deficient number. In number theory, a deficient number or defective number is a positive integer n for which the sum of divisors of n is less than 2n. Equivalently, it is a number for which the sum of proper divisors (or aliquot sum) is less than n. For example, the proper divisors of 8 are 1, 2, and 4, and their sum is less than 8, so 8 is ...

  9. Integer factorization - Wikipedia

    en.wikipedia.org/wiki/Integer_factorization

    Every positive integer greater than 1 is either the product of two or more integer factors greater than 1, in which case it is called a composite number, or it is not, in which case it is called a prime number. For example, 15 is a composite number because 15 = 3 · 5, but 7 is a prime number because it cannot be decomposed in this way.