IMO Shortlist 1991 problem 11
Dodao/la:
arhiva2. travnja 2012. Let
![S = \{1,2,3,\cdots ,280\}](/media/m/1/f/b/1fb0890b131d41473189ced47bb06df1.png)
. Find the smallest integer
![n](/media/m/a/e/5/ae594d7d1e46f4b979494cf8a815232b.png)
such that each
![n](/media/m/a/e/5/ae594d7d1e46f4b979494cf8a815232b.png)
-element subset of
![S](/media/m/c/6/3/c63593c3ec0773fa38c2659e08119a75.png)
contains five numbers which are pairwise relatively prime.
%V0
Let $S = \{1,2,3,\cdots ,280\}$. Find the smallest integer $n$ such that each $n$-element subset of $S$ contains five numbers which are pairwise relatively prime.
Izvor: Međunarodna matematička olimpijada, shortlist 1991