Hasse diagram

The positive divisors (bigger than 1) of an integer are pictured in a Hasse diagram as follows: Two divisors b and c are connected by a path going up if b is a divisor of c. Give various numbers as input and try to anwer the following questions: What are the numbers at the bottom of the diagram? For what kind of number does the diagram consist of just one node? For what kind of numbers do you get a string diagram?