A set partition of a set is a collection of disjoint subsets of whose union is . The number of partitions of the set is called a Bell number.
Set Partition
See also
Bell Number, Block, Partition, Restricted Growth String, Stirling Number of the Second KindExplore with Wolfram|Alpha
References
Ruskey, F. "Info About Set Partitions." http://www.theory.csc.uvic.ca/~cos/inf/setp/SetPartitions.html.Cite this as:
Weisstein, Eric W. "Set Partition." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/SetPartition.html