Let 1≤a₁<a₂<…<a_k<n be a sequence of integers such that gcd(a_i,a_j)=1 for all 1≤i<j≤k. What is the maximum value of k?

The best solution was submitted by Yeon Sig Lyu (류연식), 2008학번. Congratulations!

Here is his Solution of Problem 2009-17.

Alternative solutions were submitted by Prach Siriviriyakul (2009학번, +3), 정성구 (수리과학과 2007학번, +3), 김치헌 (수리과학과 2006학번, +3), 옥성민 (수리과학과 2003학번, +3).