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RMO KV P-4

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October 29, 2023
Digitsnumber theorycombinatorics

Problem Statement

The set XX of NN four-digit numbers formed from the digits 1,2,3,4,5,6,7,81,2,3,4,5,6,7,8 satisfies the following condition:
for any two different digits from 1,2,3,4,,6,7,81,2,3,4,,6,7,8 there exists a number in XX which contains both of them. \\
Determine the smallest possible value of NN.
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