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multiset permutation

An arrangement of items where some are identical copies, counted by dividing out each repeated group's internal reorderings.

A multiset permutation of n items in groups of n_1,\ldots,n_k identical copies has \dfrac{n!}{n_1!\cdots n_k!} distinct arrangements.

Examples

  • The word BANANA (3 A's, 2 N's) has 6!/(3! \cdot 2!)=60 distinct arrangements.

See also

overcounting
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