Chiheon Kim (김치헌)

Let \(a_1\le a_2\le \cdots \le a_n\) be integers. Prove that

\(\displaystyle\prod_{1\le j<i\le n} \frac{a_i-a_j}{i-j}\)

is an integer.

The best solution was submitted by Chiheon Kim (김치헌), 수리과학과 2006학번. Congratulations!

Click here for his Solution of Problem 2009-1.