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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.)
answer Comment 10 of 10 |
The required smallest number is 200.
  Posted by K Sengupta on 2007-11-23 04:29:11
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