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(just those submitted by Opao)
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+ 444444444 is the only nine-digit repdigit such that the product of itself and all truncations of itself minus one is prime. I.e., 444444444*44444444*4444444*444444*44444*4444*444*44*4 - 1 is prime. There are no such ten-digit repdigits. [Opao]




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