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Combinatorics Difficulty 5.5 AIME, harder Prove it Belarus
We call a coloring of an m×n table (m,n≥5) in three colors a good coloring if the following two conditions are satisfied:
1) Each cell has the same number of neighboring cells of two other colors;
2) Each corner cell has no neighboring cells of its color.
Find all pairs (m,n) (m,n≥5) for which there exists a good coloring of m×n table.
Solution
Answer: all (m,n) such that 6 divides both of them.
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