stirling2(m, n)

Stirling numbers of the 2nd kind: the number of ways to partition n elements into k groups

Stirling numbers of the 2nd kind show the number of ways in which a set of m elements can be clustered to form n groups. This algorithm uses a recursive formula that is exact up to intmax('uint64'). Stirling numbers under this will be represented exactly and any number larger than this but less than realmax will be approximated using double precision (16-digits). Exact solutions are available for any n in S(26,n), and for select n in S(>26,n) for select n. Solutions are available for S(<220,n) for all n, and S(>=220,n) for select n.