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OSN 2007 Problem 4

    A 10-digit arrangement 0,1,2,3,4,5,6,7,8,90,1,2,3,4,5,6,7,8,9 is called beautiful if (i) when read left to right, 0,1,2,3,40,1,2,3,4 form an increasing sequence, and 5,6,7,8,95,6,7,8,9 form a decreasing sequence, and (ii) 00 is not the leftmost digit. For example, 98071236549807123654 is a beautiful arrangement. Determine the number of beautiful arrangements.

    Dataset text AI-MO AoPS. Quoted with source.

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