Bell Numbers
Bell Numbers are a sequence of numbers that represent the number of ways to partition a set into non-empty subsets. For example, the first few Bell Numbers are 1, 1, 2, 5, and 15, which correspond to the partitions of sets with 0, 1, 2, 3, and 4 elements, respectively.
These numbers are named after the mathematician Eric Temple Bell, who studied them in the early 20th century. Bell Numbers can be calculated using a recursive formula or through Stirling Numbers, which count the ways to partition a set into a specific number of subsets.