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  2. Permutation codes - Wikipedia

    en.wikipedia.org/wiki/Permutation_Codes

    A main problem in permutation codes is to determine the value of (,), where (,) is defined to be the maximum number of codewords in a permutation code of length and minimum distance . There has been little progress made for 4 ≤ d ≤ n − 1 {\displaystyle 4\leq d\leq n-1} , except for small lengths.

  3. Birthday problem - Wikipedia

    en.wikipedia.org/wiki/Birthday_problem

    The birthday paradox refers to the counterintuitive fact that only 23 people are needed for that probability to exceed 50%. The birthday paradox is a veridical paradox: it seems wrong at first glance but is, in fact, true. While it may seem surprising that only 23 individuals are required to reach a 50% probability of a shared birthday, this ...

  4. Lehmer code - Wikipedia

    en.wikipedia.org/wiki/Lehmer_code

    In mathematics and in particular in combinatorics, the Lehmer code is a particular way to encode each possible permutation of a sequence of n numbers. It is an instance of a scheme for numbering permutations and is an example of an inversion table. The Lehmer code is named in reference to D. H. Lehmer, [1] but the code had been known since 1888 ...

  5. Diehard tests - Wikipedia

    en.wikipedia.org/wiki/Diehard_tests

    The name is based on the birthday paradox. Choose m birthdays in a year of n days. List the spacings between the birthdays. If j is the number of values that occur more than once in that list, then j is asymptotically Poisson-distributed with mean m 3 / (4n).

  6. Combinations and permutations - Wikipedia

    en.wikipedia.org/wiki/Combinations_and_permutations

    Combinations and permutations in the mathematical sense are described in several articles. Described together, in-depth: Twelvefold way; Explained separately in a more accessible way: Combination; Permutation; For meanings outside of mathematics, please see both words’ disambiguation pages: Combination (disambiguation) Permutation ...

  7. List of permutation topics - Wikipedia

    en.wikipedia.org/wiki/List_of_permutation_topics

    Toggle Permutation groups and other algebraic structures subsection. 3.1 Groups. 3.2 Other algebraic structures. 4 Mathematical analysis. ... Code of Conduct; Developers;

  8. Random permutation statistics - Wikipedia

    en.wikipedia.org/wiki/Random_permutation_statistics

    An involution is a permutation σ so that σ 2 = 1 under permutation composition. It follows that σ may only contain cycles of length one or two, i.e. the exponential generating function g(z) of these permutations is [1]

  9. Rencontres numbers - Wikipedia

    en.wikipedia.org/wiki/Rencontres_numbers

    For n ≥ 0 and 0 ≤ k ≤ n, the rencontres number D n, k is the number of permutations of { 1, ..., n } that have exactly k fixed points. For example, if seven presents are given to seven different people, but only two are destined to get the right present, there are D 7, 2 = 924 ways this could happen.