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Never prime! (Posted on 2004-04-29) Difficulty: 3 of 5
12 can be made into a prime by changing the 2 to 3; likewise, 63 can be changed into a prime by changing the 6 to 7.

What is the smallest number that cannot changed into a prime by changing a single digit?

Are there infinitely many such numbers?

See The Solution Submitted by Federico Kereki    
Rating: 3.8333 (6 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Some Thoughts re(2): Another thought - A simple solution for the 2nd part | Comment 8 of 10 |
(In reply to re: Another thought - A simple solution for the 2nd part by Ryan)

If you add eleven, you would be changing TWO digits at the same time.
  Posted by Federico Kereki on 2004-04-30 18:25:55

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