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  2. Table of divisors - Wikipedia

    en.wikipedia.org/wiki/Table_of_divisors

    The tables below list all of the divisors of the numbers 1 to 1000. A divisor of an integer n is an integer m, for which n/m is again an integer (which is necessarily also a divisor of n). For example, 3 is a divisor of 21, since 21/7 = 3 (and therefore 7 is also a divisor of 21). If m is a divisor of n, then so is −m. The tables below only ...

  3. Divisor function - Wikipedia

    en.wikipedia.org/wiki/Divisor_function

    When z is 1, the function is called the sigma function or sum-of-divisors function, [1] [3] and the subscript is often omitted, so σ(n) is the same as σ 1 (n) (OEIS: A000203). The aliquot sum s ( n ) of n is the sum of the proper divisors (that is, the divisors excluding n itself, OEIS : A001065 ), and equals σ 1 ( n ) − n ; the aliquot ...

  4. Divisor - Wikipedia

    en.wikipedia.org/wiki/Divisor

    1, −1, and are known as the trivial divisors of . A divisor of n {\displaystyle n} that is not a trivial divisor is known as a non-trivial divisor (or strict divisor [ 6 ] ). A nonzero integer with at least one non-trivial divisor is known as a composite number , while the units −1 and 1 and prime numbers have no non-trivial divisors.

  5. Colossally abundant number - Wikipedia

    en.wikipedia.org/wiki/Colossally_abundant_number

    Sigma function σ 1 (n) up to n = 250 Prime-power factors. In number theory, a colossally abundant number (sometimes abbreviated as CA) is a natural number that, in a particular, rigorous sense, has many divisors. Particularly, it is defined by a ratio between the sum of an integer's divisors and that integer raised to a power higher than one ...

  6. Untouchable number - Wikipedia

    en.wikipedia.org/wiki/Untouchable_number

    The number 5 is untouchable, as it is not the sum of the proper divisors of any positive integer: 5 = 1 + 4 is the only way to write 5 as the sum of distinct positive integers including 1, but if 4 divides a number, 2 does also, so 1 + 4 cannot be the sum of all of any number's proper divisors (since the list of factors would have to contain ...

  7. Amicable numbers - Wikipedia

    en.wikipedia.org/wiki/Amicable_numbers

    In mathematics, the amicable numbers are two different natural numbers related in such a way that the sum of the proper divisors of each is equal to the other number. That is, s(a)=b and s(b)=a, where s(n)=σ(n)-n is equal to the sum of positive divisors of n except n itself (see also divisor function). The smallest pair of amicable numbers is ...

  8. Pillai's arithmetical function - Wikipedia

    en.wikipedia.org/wiki/Pillai's_arithmetical_function

    where, is the divisor function, and is the Möbius function. This multiplicative arithmetical function was introduced by the Indian mathematician Subbayya Sivasankaranarayana Pillai in 1933. [ 3 ]

  9. Greatest common divisor - Wikipedia

    en.wikipedia.org/wiki/Greatest_common_divisor

    The greatest common divisor (GCD) of integers a and b, at least one of which is nonzero, is the greatest positive integer d such that d is a divisor of both a and b; that is, there are integers e and f such that a = de and b = df, and d is the largest such integer.