Question 128
A *special* set is a set of positive odd integers no element of which divides another, and each 3-element subset of which has a member dividing the sum of the other two. A *special* set is *maximal* if it is contained in no other *special* set. Determine the number of elements a maximal *special* set may have.
Yu. I. Ionin, Russia
Yu. I. Ionin, Russia