stirling numbers of the second kind are used to determine how many ways an n-set can be partitioned into m non-empty subsets. it goes a little something like this..

```                                    m
0      1      2      3      4      5      6      7      8      9..
________________________________________________________________________
0| 1
1| 0      1
2| 0      1      1
3| 0      1      3      1
4| 0      1      7      6      1
n 5| 0      1      15     25     10     1
6| 0      1      31     90     65     15     1
7| 0      1      63     301    350    140    21     1
8| 0      1      127    966    1701   1050   266    28     1
9| 0      1      255    3025   7770   6951   2646   462    36     1
:|
```
these numbers are also sometimes represented in a triangle, since half the chart is empty where m > n, that is, where the number of partitions is 0. how do you get these numbers (if, for example, you wanted to fill in row 10)? a general rule for filling in the chart is S(n,m) = (n-1,m-1) + m(n-1,m).