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MathNet 2009-part-04 — 175 problems (EN–VI) Question 1

Math Olympiad Vault · MathNet 2009-part-04 — 175 problems (EN–VI)

Question 1

Let $n \ge 4$ be a positive integer. Into every square of an $n \times n$ array we inscribe an integer so that the sum of the integers inside any $3 \times 3$ square is negative. Find all positive integers $n$ for which this can be done in such a way that the sum of all the numbers in the array is positive.