Must be a multiple of 4
Must be a multiple of 6
Since workers can return an assignment or drop out, some "spare" participants will be created: the oTree session will have 2 times more participant objects than the number you enter here.
You can make more properties configurable by adding them to your session config in settings.py.
a.k.a. Keynesian beauty contest. Players all guess a number; whoever guesses closest to 2/3 of the average wins. See https://en.wikipedia.org/wiki/Guess_2/3_of_the_average