Problem:
Compute the number of positive integers that divide at least two of the integers in the set .
Problem:
Compute the number of positive integers that divide at least two of the integers in the set .
Solution:
For a positive integer , let be the product of the distinct prime factors of . Observe that if , all prime factors of must divide , so .
Therefore, if is such an integer, must divide at least two of the numbers in , implying that is either , or . These have , and cases, respectively, for a total of .