An element.
The objects within a number set can be caled as "Elements" or "members".
That's called the "solution set".
Since there are 9 members in the given set there will be 29 = 512 subsets and I have neither the time nor inclination to list all 512 of them. A subset of the given set is any set all of whose members are members of the given set. This includes the null set. To start off: Null, {1}, {3}, {6}, etc {1,3}, {1,6}, {1,12}, etc {1,3,6}, (1,3,12}, etc etc
a set whose members are other members of another set a set contained within them