Let COL be a 3-coloring of the numbers 1, …, 2006. Show that there exist numbers X and Y such that COL(X) = COL(Y) and |X − Y| is a square. Appeared on Maryland Math Olympiad 2006. Acquired from Luca Trevisan’s blog.
A 3-coloring is an assignment of one color (of possible three colors) to each number. So e.g. fix some three colors Red, Green and Blue and then a 3-coloring of the numbers 1, 2, 3, 4 and 5 could be say: 1->R, 2->G, 3->R, 4->B, 5->B.
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What is a 3-colouring of numbers?
A 3-coloring is an assignment of one color (of possible three colors) to each number. So e.g. fix some three colors Red, Green and Blue and then a 3-coloring of the numbers 1, 2, 3, 4 and 5 could be say: 1->R, 2->G, 3->R, 4->B, 5->B.
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