puzzle

[brickviking]

(06-29-2018 03:40 AM)Don Shepherd Wrote:  How many 4-digit arrangements of the digits of the number 1232 are prime?

How many 4-digit arrangements would you have to check?

Is there a way to check other than an electronic prime factor finder or our old friend, brute force?

Before I read any other posts, there are only two arrangements you'd have to check. The rest are not prime. Now I'd better go read the rest of the thread...

(Later) I'd forgotten about a couple of the others, and was basing my theory on anything ending in 1 or 3, regardless of what the other digits were. My only mistake was that not all the possible numbers began with 22. :/

Personally, I'd just do it by brute force, there aren't that many combinations to check.

(Post 253)