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  2. Eulerian number - Wikipedia

    en.wikipedia.org/wiki/Eulerian_number

    The permutations of the multiset {,,,, …,,} which have the property that for each k, all the numbers appearing between the two occurrences of k in the permutation are greater than k are counted by the double factorial number ()!!.

  3. Inversion (discrete mathematics) - Wikipedia

    en.wikipedia.org/wiki/Inversion_(discrete...

    The identity is its minimum, and the permutation formed by reversing the identity is its maximum. If a permutation were assigned to each inversion set using the element-based definition, the resulting order of permutations would be that of a Cayley graph, where an edge corresponds to the swapping of two elements on consecutive places. This ...

  4. Multiset - Wikipedia

    en.wikipedia.org/wiki/Multiset

    A multiset may be formally defined as an ordered pair (A, m) where A is the underlying set of the multiset, formed from its distinct elements, and : + is a function from A to the set of positive integers, giving the multiplicity – that is, the number of occurrences – of the element a in the multiset as the number m(a).

  5. Permutation - Wikipedia

    en.wikipedia.org/wiki/Permutation

    Single-track Gray code: [63] each column is a cyclic shift of the other columns, plus any two consecutive permutations differ only in one or two transpositions. Nested swaps generating algorithm in steps connected to the nested subgroups +. Each permutation is obtained from the previous by a transposition multiplication to the left.

  6. Stirling permutation - Wikipedia

    en.wikipedia.org/wiki/Stirling_permutation

    In combinatorial mathematics, a Stirling permutation of order k is a permutation of the multiset 1, 1, 2, 2, ..., k, k (with two copies of each value from 1 to k) with the additional property that, for each value i appearing in the permutation, any values between the two copies of i are larger than i. For instance, the 15 Stirling permutations ...

  7. Inclusion–exclusion principle - Wikipedia

    en.wikipedia.org/wiki/Inclusion–exclusion...

    In the given example, there are 12 = 2(3!) permutations with property P 1, 6 = 3! permutations with property P 2 and no permutations have properties P 3 or P 4 as there are no restrictions for these two elements. The number of permutations satisfying the restrictions is thus: 4! − (12 + 6 + 0 + 0) + (4) = 24 − 18 + 4 = 10.

  8. Twelvefold way - Wikipedia

    en.wikipedia.org/wiki/Twelvefold_way

    In combinatorics, the twelvefold way is a systematic classification of 12 related enumerative problems concerning two finite sets, which include the classical problems of counting permutations, combinations, multisets, and partitions either of a set or of a number.

  9. Derangement - Wikipedia

    en.wikipedia.org/wiki/Derangement

    This is the limit of the probability that a randomly selected permutation of a large number of objects is a derangement. The probability converges to this limit extremely quickly as n increases, which is why !n is the nearest integer to n!/e. The above semi-log graph shows that the derangement graph lags the permutation graph by an almost ...