Set Partition

A set partition of a Set $S$ is a collection of disjoint Subsets of $S$ whose Union is $S$. The number of partitions of the Set $\{k\}_{k=1}^n$ is called a Bell Number.

See also Bell Number, Block, Restricted Growth String, Stirling Number of the Second Kind

References

Ruskey, F. ``Info About Set Partitions.'' http://sue.csc.uvic.ca/~cos/inf/setp/SetPartitions.html.