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?

(In reply to A simple solution for the 2nd part by e.g.)

Nice.  Much more elegant.   (of course, it doesn't pay homage to the smallest theme of the other part...)  It seems my solution never got posted......  This site is working against me.  ;-)

Posted by Ryan on 2004-04-30 14:52:29