# Multiset

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A multiset is a collection of unordered objects.

Unlike sets, elements of multisets need not be distinct.

## Multiset coefficient

The number of multisets of size $k$ taken from a set of cardinality $n$ is denoted by the multiset coefficient, denoted by $\left(\!\!\tbinom{n}{k}\!\!\right)$ , and is equal to:

$\left(\!\!\binom{n}{k}\!\!\right)=\binom{n+k-1}{k}=\binom{n+k-1}{n-1}$