My friend was thinking of a 3digit prime number. I asked him, "What are the last two digits of your number?" He answered, and I knew what the number was. What was the number?
The friend was thinking of 389.
389 is the only 3digit prime number that ends with the digits 8 and 9. All other digit pairs exist in more than one 3digit prime  except where leading zeroes are permitted, in which case 002 ending in digits 0 and 2, and 005 ending in digits 0 and 5 are also unique digit pairs in 3digit primes. Yet, it is inferred the solution is unique, thus the implication is that leading zeroes are not permitted.

Posted by Dej Mar
on 20110127 18:09:08 