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QuikSand
08-08-2003, 08:23 AM
Primes are always a weird source of math conjecture - but this one doesn't involve any real higher-order thinking, I don't think.

Take a number like 54. It's not prime, of course, but if we changed one digit, we could make it into a prime. In this case, if we adjust the digit 4 into a 3, we get 53 - which is a prime. (We also could have adjusted the 4 into a 9 - it doesn't have to be an adjustment by any particular incremnt - just a change to any other single digit)

The puzzle is this: what is the smallest number that cannot be changed into a prime by modifying one of its digits?
Bonegavel
08-08-2003, 08:24 AM
21

[edit: sorry, I thought this was another Quik gambling thread. My eyes glazed over after the first sentence of post and I made the rest up myself. I thought we were playing BlackJack.]
mrsimperless
08-08-2003, 08:27 AM
202
Alan T
08-08-2003, 08:28 AM
200 ?
mrsimperless
08-08-2003, 08:30 AM
Figures I would find the SECOND lowest one...

:rolleyes:


Nice job Alan, I'm guessing that you found it.
Alan T
08-08-2003, 08:34 AM
I guess it shows though that it took me 1 minute longer to count prime numbers than you :)
mrsimperless
08-08-2003, 08:38 AM
Not really. I, um.... used a resource. ;)

Prime numbers list (http://www.utm.edu/research/primes/lists/small/10000.txt)
Bee
08-08-2003, 08:44 AM
2/3
Alan T
08-08-2003, 08:48 AM
Originally posted by mrsimperless
Not really. I, um.... used a resource. ;)

Prime numbers list (http://www.utm.edu/research/primes/lists/small/10000.txt)

Doh :)
QuikSand
08-08-2003, 09:43 AM
200 is correct, of course. Nicely done.