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MathNet 2008-part-02 — 165 problems (EN–VI) Question 14

Math Olympiad Vault · MathNet 2008-part-02 — 165 problems (EN–VI)

Question 14

In the coordinate plane consider the set $S$ of all points with integer coordinates. For a positive integer $k$, two distinct points $A, B \in S$ will be called $k$-friends if there is a point $C \in S$ such that the area of the triangle $A B C$ is equal to $k$. A set $T \subset S$ will be called a $k$-clique if every two points in $T$ are $k$-friends. Find the least positive integer $k$ for which there exists a $k$-clique with more than 200 elements.