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MathNet 2019-part-01 — 184 problems (EN–VI) Question 76

Math Olympiad Vault · MathNet 2019-part-01 — 184 problems (EN–VI)

Question 76

Determine if there is an integer $k \ge 2$ such that if we partition the set $\{2, 3, \dots, k\}$ in two parts, then at least one of the parts contains numbers $a, b$ and $c$ with $ab = c$? (We allow $a = b$.) If such a number $k$ exist, find the least $k$ with this property.