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15

Part of PEN N Problems

Problems(1)

N 14

Source:

5/25/2007
In the sequence 0000, 0101, 0202, 0303, ⋯\cdots, 9999 the terms are rearranged so that each term is obtained from the previous one by increasing or decreasing one of its digits by 11 (for example, 2929 can be followed by 1919, 3939, or 2828, but not by 3030 or 2020). What is the maximal number of terms that could remain on their places?
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