Interesting problem. Got it after a brief bit of futzing with a Ruby shell. There’s likely a much more efficient and elegant solution than mine. I selected all primes between 123456 and 987654, then used regular expressions to check the rules about neighboring or repeated digits, and then checked the last rule by hand on the 11 remaining possibilities.

Seeing as I haven’t programed in years, I did this out by hand. Starting from the lowest possible number and working my way up, I found that there was actually a pretty small range of numbers that worked. I also used WolframAlpha to eliminate some of the tedium.

Started with a web-acquired a list of all 6 digit primes, and a manually assembled matrix of allowed neighbors from rules 5,6,&7. From there it was less trouble (for me, anyway) to write out the comparison loops than to work out regexps. The java program takes a blink of an eye to run.

I am confused about what you meant by “neighboring digits must not share factors”. I thought every possible number shares 1 as a factor and that 0 could be factored by any number.

I solved it by hand, practically by accident. I didn’t know how to check primes, so I constructed a 6-digit number that followed the rules, then punched it in. Not prime. Reversed two of the odd digits and tried again. Got it.

I am absolutely 100% bamboozled. I can’t find any rules or logic puzzle or anything that everyone else on this page seems to have found. All I see is a log-in prompt.

It’s a little confusing, Nic, but if you go to “Create Account” and “help” it gives you rules for creating a password. Thus, SZYGLIA (or whatever) must have a pasword that follows those rules.

@interested: Are you sure? Could you post this second regular password, which isn’t the password of SZYGLIA? Yes, I’m a smart alec (I hope I don’t err!), and this isn’t my native language.

Well doing it by hand was surprisingly easy. When you consider the digits a prime can end in, working out all the possible numbers backwards and then checking to see if they are prime only took like 20 minutes.

## 28 Comments

123456 (increpare edit: I changed it, it was too close to being a total spoiler : P )

Interesting problem. Got it after a brief bit of futzing with a Ruby shell. There’s likely a much more efficient and elegant solution than mine. I selected all primes between 123456 and 987654, then used regular expressions to check the rules about neighboring or repeated digits, and then checked the last rule by hand on the 11 remaining possibilities.

I don’t think there’s a nicer way, really. I probably could have thought of some sexier constraints.

Is zero ever used?

Maybe.

My math knowledge is pretty limited, so I’d appreciate some help. What rules does 253819 break?

two pairs of odd digits side by side (53, 19)

Seeing as I haven’t programed in years, I did this out by hand. Starting from the lowest possible number and working my way up, I found that there was actually a pretty small range of numbers that worked. I also used WolframAlpha to eliminate some of the tedium.

It was a fun logic game.

Heheh. Good that it wasn’t too intractable : )

Started with a web-acquired a list of all 6 digit primes, and a manually assembled matrix of allowed neighbors from rules 5,6,&7. From there it was less trouble (for me, anyway) to write out the comparison loops than to work out regexps. The java program takes a blink of an eye to run.

Catnip for geeks! :^)

i’m not speaking natively english but french, and desperate about finding a translation for “non-trivial” in its mathematical meaning.

is it something like “non premier” ?

“no non-trivial divisors” = prime number – pretty sure it translates as premier

I am confused about what you meant by “neighboring digits must not share factors”. I thought every possible number shares 1 as a factor and that 0 could be factored by any number.

Informal ambiguity is not necessarily insurmountable.

I solved it by hand, practically by accident. I didn’t know how to check primes, so I constructed a 6-digit number that followed the rules, then punched it in. Not prime. Reversed two of the odd digits and tried again. Got it.

My much smarter friend hates me now.

I am absolutely 100% bamboozled. I can’t find any rules or logic puzzle or anything that everyone else on this page seems to have found. All I see is a log-in prompt.

It’s a little confusing, Nic, but if you go to “Create Account” and “help” it gives you rules for creating a password. Thus, SZYGLIA (or whatever) must have a pasword that follows those rules.

technically, the system can only have two correct passwords if all the rules are applied. Pretty trashy password rules if you ask me :P

Thanks for this fun puzzle.

@interested: Are you sure? Could you post this second regular password, which isn’t the password of SZYGLIA? Yes, I’m a smart alec (I hope I don’t err!), and this isn’t my native language.

Posted solutions will be censored.

Actually I just wanted to know wether there are multiple solutions or not (or rather i wanted to claim that there aren’t), since I’ve found only one.

@wurfmaul I think he was mistaken and thought an invalid password worked. Maybe it wasn’t prime.

Where can I find the rules? Eric S referred to rules 5, 6 and 7. Where are they?

You can find them. I believe in you.

:’) Thanks. Deeply touching words. I’ll try harder, I promise

I found the rules, and one solution: if imposible were numbers 0 win :)

Cool, not going to try to figure it out, though.

Well doing it by hand was surprisingly easy. When you consider the digits a prime can end in, working out all the possible numbers backwards and then checking to see if they are prime only took like 20 minutes.