IMO Shortlist 1969 problem 40
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Avg: 0,0 Find the number of five-digit numbers with the following properties: there are two pairs of digits such that digits from each pair are equal and are next to each other, digits from different pairs are different, and the remaining digit (which does not belong to any of the pairs) is different from the other digits.
Izvor: Međunarodna matematička olimpijada, shortlist 1969