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Non-Dividing Sets

Submitted by Geoff, 30 July 2002. Original answer and this article by Allen Stenger.

I am asked to find the largest number of elements that a set of integers from 1 through 100 can have so that no one element in the set is divisible by another. I was told a "hint:" Imagine all the numbers 1--100 in the form (2^k) * m where k ≥ 0 and m is odd. I have DONE this for nearly all the integers 1--100 but cannot see a viable pattern. I don`t want the answer to this question just help interpreting the hint or maybe some insight into a nother way to solve it. Any help would be great. Thanks!

Hint 1

Work on the following more general problem: Among the set of integers from 1 through 2n, what is the largest subset such that no element divides another element? The reason this is a better problem is that

  • you can practice on smaller examples, such as n = 1, n = 2, n = 3;
  • there`s a very strong pattern in the answers, which you should be able to figure out from the small cases before you have to tackle the big case of n = 50.

Need another hint? Click here.

Click here for the complete solution.


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