Problems & Puzzles:
Composites that remain composites when...
The number 200 is the minimum number that
changing a single digit remains composite (See
http://oeis.org/A118118 and also
Q. Find the minimum odd composite number
not ending in 5 that remains composite changing at a time any
two digits by any of the 10x10 combinations of integers 0 to 9,
or show that it does not exists.
Contributions came from Gérald DeGroote
In puzzle 714, I don't understand this :
is the minimum number that changing a single digit remains composite"
but if we change the digit 2 by
0, it gives us the number "000", which is neither composite nor