Someone know how to compute in how many ways is it possible to partition a collection of indistinguishable elements in groups (evidently with at least one element for each groups)???

The groups are distinguishable; I mean, if and the solution is 2 combinations (1,2) and (2,1) (whereas (3,0) and (0,3) are not allowed since a group is empty)

( probably related to this thread

http://www.mathhelpforum.com/math-he...subgroups.html )