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  2. Factorial - Wikipedia

    en.wikipedia.org/wiki/Factorial

    [39] [40] The factorial number system is a mixed radix notation for numbers in which the place values of each digit are factorials. [ 41 ] Factorials are used extensively in probability theory , for instance in the Poisson distribution [ 42 ] and in the probabilities of random permutations . [ 43 ]

  3. Factorial number system - Wikipedia

    en.wikipedia.org/wiki/Factorial_number_system

    The factorial number system is sometimes defined with the 0! place omitted because it is always zero (sequence A007623 in the OEIS). In this article, a factorial number representation will be flagged by a subscript "!". In addition, some examples will have digits delimited by a colon. For example, 3:4:1:0:1:0! stands for

  4. Double factorial - Wikipedia

    en.wikipedia.org/wiki/Double_factorial

    In mathematics, the double factorial of a number n, denoted by n‼, is the product of all the positive integers up to n that have the same parity (odd or even) as n. [1] That is, n ! ! = ∏ k = 0 ⌈ n 2 ⌉ − 1 ( n − 2 k ) = n ( n − 2 ) ( n − 4 ) ⋯ . {\displaystyle n!!=\prod _{k=0}^{\left\lceil {\frac {n}{2}}\right\rceil -1}(n-2k ...

  5. Falling and rising factorials - Wikipedia

    en.wikipedia.org/wiki/Falling_and_rising_factorials

    In mathematics, the falling factorial ... gives the number of n-permutations ... The rising factorial is also integral to the definition of the hypergeometric ...

  6. Derangement - Wikipedia

    en.wikipedia.org/wiki/Derangement

    (n factorial) is the number of n-permutations; !n (n subfactorial) is the number of derangements – n-permutations where all of the n elements change their initial places. In combinatorial mathematics , a derangement is a permutation of the elements of a set in which no element appears in its original position.

  7. Permutation - Wikipedia

    en.wikipedia.org/wiki/Permutation

    The sum of the numbers in the factorial number system representation gives the number of inversions of the permutation, and the parity of that sum gives the signature of the permutation. Moreover, the positions of the zeroes in the inversion table give the values of left-to-right maxima of the permutation (in the example 6, 8, 9) while the ...

  8. Unique factorization domain - Wikipedia

    en.wikipedia.org/wiki/Unique_factorization_domain

    In mathematics, a unique factorization domain (UFD) (also sometimes called a factorial ring following the terminology of Bourbaki) is a ring in which a statement analogous to the fundamental theorem of arithmetic holds.

  9. Primorial - Wikipedia

    en.wikipedia.org/wiki/Primorial

    In mathematics, and more particularly in number theory, primorial, denoted by "p n #", is a function from natural numbers to natural numbers similar to the factorial function, but rather than successively multiplying positive integers, the function only multiplies prime numbers.