Sorry for the confusing title, I’ll elaborate with an example.
You have been assigned group #4, and you are curious how many groups in total there are. Assuming groups are numbered sequentially starting at 1 and group assignment is random, you can assume there are at least 4 groups.
So far, I know that the most probable number of groups is your group number. You are more likely to be in group 4 if there are 4 groups, than if there were 1000. There is some kind of decay model where the larger the guess, the less probable it is, but I can’t figure it out. Whatever the probability model is, the area under it should equal 1.