# Talk:Substring primes

## different than truncatable primes?

How does this differ from truncatable primes?--Nigel Galloway (talk) 15:07, 5 April 2021 (UTC)

It's a smaller list,   it includes substrings that are not truncatable.     -- Gerard Schildberger (talk) 15:39, 5 April 2021 (UTC)
See the OEIS entry:   A024770 right-truncatable primes.
See the OEIS entry:   A024785 left-truncatable primes.
See the OEIS entry:   A085823 numbers in which all substrings are primes.

If I create a set of primes less than 500 then filter such that for each member n the set contains n%10 shall I have completed this task with no prime tests?--Nigel Galloway (talk) 15:23, 8 April 2021 (UTC)

There seems to be a disagreement concerning what   is   a primality test,  so I will defer an opinion.     -- Gerard Schildberger (talk) 16:17, 8 April 2021 (UTC)
Nice try, but I think "the set contains" is itself a primality test, no? And is generating those 95 primes itself 500 primality tests? Admittedly that is slightly flawed logic since they would probably be quietly generated somewhere anyway. Also bear in mind this all started when I tried to find solutions > 373 when there aren't any... I have no problem with you or anyone else improving this task, although I stand by my claim that a limit of 500 is at best "misleading". --Pete Lomax (talk) 17:09, 8 April 2021 (UTC)

## limit

Removed utterly pointless limit of 500. Find 'em all, it's the same output, and encourages a little more thought than for i=1 to 500. --Pete Lomax (talk) 08:54, 6 April 2021 (UTC)

By removing the task's limit, you're invalided all but "your" solution.   The whole point of Rosetta Code   (well, at least one of them)   is to compare how different computer programming languages (and programmers) solve the stated problem (the task as stated).   Significantly changing the (draft) task's requirements (and/or wording) makes comparing the solutions at this point, pointless.   At this time, all but one programming solution uses a limit of some kind.     -- Gerard Schildberger (talk) 10:26, 6 April 2021 (UTC)
They are not invalidated at all, they all give the correct output, apart from the REXX entry which blatently lies about how many prime tests it performs (it's 26 btw, or 119 if you also count the digit-wise exclusions). Using a limit is a valid way to do it, just not a very smart one. I was only trying to make a rather pedestrian task into something slightly more interesting/challenging, optionally. If you want to change it to something like "This can be achieved by filtering all primes below 500 (there are 95 of them), but it can also be done by only checking 15 numbers." then I'll not complain. --Pete Lomax (talk) 13:34, 6 April 2021 (UTC)
The REXX entry does give the correct output.   Apart from your characterization of how (and what) the REXX entry counts as primality testing,   and I   (as the sole author of the REXX entry)   shouldn't be accused of being blatantly lying;   I didn't considering the elimination of various numbers using digit-wise filtering as a primality test,   but I don't want to get into useless and/or pejorative arguments about how one   counts   the number of primality tests and whether or not it was performed in a blatant manner (or not).   I added the primality counting in good faith and I don't see how you could label that as lying,   and blatant lying at that.   And, no, I do not want to change the task's requirements as per your suggesting such that you won't complain.   That's not how changing of someone else's Rosetta Code task's requirements is supposed to work.   Furthermore, please be more careful of calling people liars on Rosetta Code.     -- Gerard Schildberger (talk) 20:31, 6 April 2021 (UTC)
OK, when I said "The REXX entry blatently lies", I meant no personal attack, I am sure you made an honest mistake. Despite my very best intentions, my own documentation (and program source and RC entries) almost certainly contain dozens of "blatent lies", a term I apply liberally to my own work, and should refrain from applying to that of others. But it is worrying when the output shown is wrong, as you have just done again on Palindromic primes.
Maybe the output was correct but the code was out of date - I have not seen any REXX version that could ever have possibly output a count of 14.
Sorry, but I am completely dumbstruck by your inability to comprehend new vs. modified task, and cannot say anything that would make that any clearer. --Pete Lomax (talk) 13:48, 7 April 2021 (UTC)
```                            In other words how is (no task -> task) actually any different to (task -> modified task), really?
```                             (Against my better judgement, but I've had enough of this nonsense, and