This problem states:

...find the largest subset such that every

pair(Si, Sj) of elements in this subset satisfies: Si % Sj = 0 or Sj % Si = 0.

So how could the solution set include only **one** number?

input of [2,3,5,7,11,13,17,19,23,31,1000000007] results in the expected solution of [31]!

input of [546,669] results in the expected solution of [546]!

Can someone explain why the expected solution has only one number? Why shouldn't those result in empty solutions sets?