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987 is the only 3-digit number with consecutively decreasing digits such that when multiplied by the sum of its digits plus and minus one, the results are primes. I.e., 987*(9+8+7)-1 and 987*(9+8+7)+1 are primes. [Opao]

 

  Submitted: 2003-11-19 21:14:28;   Last Modified: 2008-01-30 11:28:00.



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