Problems & Puzzles: Puzzles

Puzzle 714 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 Puzzle 679). 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.

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Contributions came from Gérald DeGroote

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Gérald wrote:

In puzzle 714, I don't understand this :

"The number 200 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 prime,...

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