I realize we have discussed Project Euler and other ongoing contests before (here and here and here and elsewhere), but I was a bit surprised a while ago when I flagged a question for moderator attention, writing "Apparently a Project Euler question, as per a comment," and got the action, "declined - What should a mod do here? Close it? You could vote to do that yourself." I thought we had a consensus that these questions should be flagged for moderator attention and should be locked by the moderator until the end of the contest. So, I misremembered the policy, or the policy changed while I wasn't looking, or else the moderators are not all on the same page.

Which is it, please?

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    $\begingroup$ I don't remember exactly, but project Euler isn't really an ongoing contest like the others? AFAIK it's a site with a list of problems that you can solve, and you don't really "win" anything if you complete them all, no? And it's not timed, most problems have been online for years. It's not too different from a textbook with a list of problems at the end... The only difference is maybe the website congratulates you when you solve a problem and keeps a completion percentage for you, but I don't think that's enough to forbid PE questions (with proper attribution obviously). $\endgroup$ Sep 11, 2015 at 7:31
  • $\begingroup$ This answer has score +11 says that mods should deal with such question in some way if one of the Project Euler organisers contacts them. $\endgroup$ Sep 11, 2015 at 7:40
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    $\begingroup$ @Martin, in one of the contest-problem discussions, Will Jagy posted email from a Project Euler organizer asking us not to answer PE questions. I think that counts as blanket contact from PE, and obviates the need for an organizer to contact a moderator every time a PE question gets posted here. $\endgroup$ Sep 11, 2015 at 8:43
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    $\begingroup$ @GerryMyerson You mean this anwer, right? I suppose that the most important thing is what the moderators say about this. (Even a if a post has score +11 or +14, that does no automatically make it an official policy of the site.) $\endgroup$ Sep 11, 2015 at 8:52
  • $\begingroup$ @Martin, I agree that a big plus score doesn't make anything an official policy. But I thought I remembered moderators acting as if it were official policy, by locking or deleting PE questions. $\endgroup$ Sep 11, 2015 at 12:18
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    $\begingroup$ If that is indeed the admin's response, summarizing it as "They asked us not to answer PE questions" is somewhat misleading. The admin in question (hk) apparently finds embarrassing that someone would post a PE question here to let other people solve the problem for them. That's it. $\endgroup$ Sep 11, 2015 at 12:18
  • $\begingroup$ @NajibIdrissi, I repeated it all as an answer here. Please compare the letter from hk to the (milder) posts on the PE forum. $\endgroup$
    – Will Jagy
    Sep 11, 2015 at 16:01
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    $\begingroup$ @WillJagy I see, it's different in tone. But as far as I understand (maybe I'm misinterpreting), the opinion presented is that the users who post PE problems here are wasting a valuable opportunity to learn. That's probably true. $\endgroup$ Sep 11, 2015 at 16:11
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    $\begingroup$ Now my opinion is that if a user posts a question in a manner suitable for math.SE (so: including context, etc) and with proper attribution, it's doesn't matter that the question came from PE. We can't force students to use the tool that PE is for them correctly, but at least we can maintain the quality of the questions posted here. A user who posts a PE problem here has pretty much given up, but the existence of a Q&A coming from PE doesn't hurt other PE users. $\endgroup$ Sep 11, 2015 at 16:13
  • $\begingroup$ @NajibIdrissi, thank you for reading it. $\endgroup$
    – Will Jagy
    Sep 11, 2015 at 16:13
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    $\begingroup$ The rule "locked until the end of the contest" doesn't work for Project Euler. So I guess the moderator is right, and we should all vote to close such problems. $\endgroup$
    – GEdgar
    Sep 16, 2015 at 15:30
  • $\begingroup$ @Inan, you might be right, I might have confused you with another user. $\endgroup$ Aug 7, 2022 at 9:35
  • $\begingroup$ @Inan, are we talking about math.meta.stackexchange.com/questions/35022/… ? $\endgroup$ Aug 7, 2022 at 9:45
  • $\begingroup$ @Inan, OK, so, on 2 August, you expressed surprise at my writing that adding stuff to another users post could get negative reactions, and asked for references, which I then gave. Then on 3 August we had the discussion you're posting about now. By the way, why did you delete that discussion from meta? $\endgroup$ Aug 7, 2022 at 22:37
  • $\begingroup$ Well, unless there's another user with the screen name @InanimateBeing, our discussion on 2 August is right there at the link I gave. $\endgroup$ Aug 8, 2022 at 9:54

4 Answers 4


Consider the following extract from our contest question policy:

What is a contest question?

For the purpose of this discussion, a contest question refers to a question that is

  1. originally published by a third party, for the purpose of inviting submission of solutions: this could be an actual competition where a prize of some sort is given, or this could be a qualifying examination.
  2. publicly available: the questions themselves should be publicly available.
  3. time-limited: the "contest" should be active for a fixed, finite duration of time, with a definite start and end date. Before the end date of the contest, the contest is said to be "on-going"; after the end date the contest is said to have "finished" or "expired."

Note in particular point (3), which states that as per our policy contests must be time-limited. As there is no limit for Project Euler problems, they do not fall under the purview of the policy.

To a great extent Project Euler questions (or questions related to Project Euler problems) should be dealt with the same way other questions are dealt with. (And let's be honest: a exceedingly small percentage of our questions do not come from some external — usually unidentified — source.) I personally see no reason to treat them separately. If they are good questions, treat them accordingly; if they are bad questions, do the same. This shouldn't require any moderator intervention.

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    $\begingroup$ For fuller disclosure, I am not personally enthralled at locking CodeChef, HackerRank or Brilliant problems under our policy, either. Were it up to me it would be reserved for more serious completitions, like the USAMTS or Bundeswettbewerb Mathematik. $\endgroup$
    – user642796
    Sep 11, 2015 at 8:08
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    $\begingroup$ The PE people have asked us not to post answers to their questions. Isn't it worth something to us to have the good will of other portions of the mathematical community? $\endgroup$ Sep 11, 2015 at 8:46
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    $\begingroup$ @GerryMyerson The Project Euler people cannot "own" questions related to the concepts which appear in their puzzles. And questions specifically asking "Can you write a Befunge program to solve...?" would be off-topic here. Much like the New York Times crossword, if someone cheats on these puzzles the only person they are really cheating is themself. I'm not certain if too much effort should be expended on protecting the integrity of Project Euler, as it is really only for the benefit of them, and not so much the mathematical community. $\endgroup$
    – user642796
    Sep 11, 2015 at 11:10
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    $\begingroup$ +1 because your answer accurately represents the current philosophy of the site and moderators (from the last time it was discussed), but -2 because I really think we should be closing PE questions instead. So, net -1. $\endgroup$
    – apnorton
    Sep 12, 2015 at 14:40
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    $\begingroup$ @apnorton I don't think that questions related to Project Euler problems should be closed just because they are so related. I fully admit that often such questions are terrible. But we have ways to deal with this which do not require moderator intervention. At the same time good, honest Project-Euler-related questions should not be punished because of this relationship. (And, last I checked, we didn't have a "Project Euler" close reason.) $\endgroup$
    – user642796
    Sep 12, 2015 at 15:18
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    $\begingroup$ @GerryMyerson: If you are talking about the letter from hk included in Will Jagy's answer, a careful reading shows that hk has not asked any such thing. $\endgroup$ Sep 13, 2015 at 19:42

Here is what I post as an answer sometimes, if I see a question quickly enough for it to make the slightest difference. I have learned to post it CW and not to reply to comments, the people who want help here for these questions want what they want and are unpleasant. Meanwhile, one may claim separation of church and state, nothing I can do about that, but hk was angry that kids were cheating his site; I can see that, on the PE forum's own public Meta, he did use the word embarrassing. His letter is stronger.

Still me: what I see is this Colin Hughes putting in an incredible amount of effort to give students (who may not have done well in a traditional class/homework/test environment) an opportunity to learn by doing, using computer programming, something they may find more natural than mathematics. From the magazine article, it is clear that some see this as a way to learn or improve programming instead. The setup is a community intended to be self contained; wide dissemination of answers for the problems undermines the process.


Magazine article by James Sommers :



discussion on MO:



discussion at Project Euler's own forum:



email letter from "hk", Novemeber 2011

Hi Will,

let me introduce myself to you. I'm hk at Project Euler. The philosophy of Colin Hughes, the founder of Project Euler was the philosophy of inductive self learning. Just Googling on the subject will reveal you quite a lot about this educational subject. (The top item on my version of Google was this one: http://mate.calpoly.edu/media/files/Review_inductive_learning.pdf)

My personal view on this matter is: if you lack the attitude, when faced with a new problem, to break it down into smaller parts or to investigate smaller cases you will never never become a successful scientist or academically schooled person. The problem in question that raised attention to Project Euler is particularly fit for scaling down and discover some useful facts.

I think we are facing a cultural clash here: The rationalisations shown to us by e.g. rbharvs are from the level: I have to be told how to do things. I'm afraid that has to do with a failing educational system that shows students rules and formulas without giving them enough room to experiment before formalising knowledge.

To do some work that is new to you, be it research mathematics or toying around with problems for which all underlying maths is known, you will need to doodle around with the problem or parts of it. How else can one do essentially new work? Top down teaching that doesn't help their students to develop this kind of ability produces people that start shouting: tell me how to do it and I will try to copy it. Some people that are badly educated in the way I sketched are just using Project Euler to develop those skills. I hope that they will benefit from that in their professional life. Some have even indicated that it was Project Euler that ultimately made them decide to choose mathematics for their academic study despite the poor level of the mathematical education in their country.

The people that posed the questions at Math Overflow, in my opinion have shown to lack the mental attitude to do the necessary doodling around. (Take for instance the fact that one of them copied the radius 10^10. Some experimenting would have shown them that ______).

Well, you can consider this private communication as lunch talk if it doesn't interest you, but I hope I gave you some information about the philosophy of Project Euler. Feel free to paraphrase it to your wish when communicating with your colleagues at Math Overflow. If you like to know more feel free to email me.

Thanks again for the effort you have invested in the case.




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    $\begingroup$ I note that the letter from hk expresses disappointment with people posting the questions, but does not express any opinion about people answering them. There is certainly nothing in that letter saying that hk would want the SE community to close or remove such questions. $\endgroup$ Sep 13, 2015 at 19:41
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    $\begingroup$ @Nate, I think there is a degree of politeness and a wish not to burden me or the websites involved. In the PE forum link, you see how hk says he will not go on MO to further vent his feelings. There is also a reticence I have sometimes seen in people who are really serious about their responsibilities in some arena: I am an important figure in my little world, I am doing my best, I cannot tell you how to behave if you are not directly part of it. $\endgroup$
    – Will Jagy
    Sep 13, 2015 at 19:59
  • $\begingroup$ That letter doesn't appear angry in the slightest. Very firmly opinionated (and well justified for being so), but not angry. What's the half-sentence, "Some experimenting would have shown them that ______"? $\endgroup$
    – Wildcard
    Jan 10, 2017 at 4:23
  • $\begingroup$ @Wildcard it was a mathematical comment on the specific PE problem that brought about the discussion. I would rather not share that with the students. I invite you to look at the discussion at the PE forum, link now repaired. $\endgroup$
    – Will Jagy
    Jan 10, 2017 at 4:40

At the moment, Project Euler has its own tag with text "Project Euler is a series of challenging mathematical/computer programming problems. Please see the site and rules before posting."

The tag legitimates asking the question. It isn't completely clear which site and which rules are meant, or what happens if those rules are transgressed.

  • $\begingroup$ Here is link to the tag-info for (project-euler). I think it is worth pointing out that the text you quoted in your post is the tag excerpt. The tag wiki for this tag has more information. $\endgroup$ Sep 18, 2015 at 6:56
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    $\begingroup$ I don't understand why there's such a tag to begin with. Why not a tag (rudin) or something like that then? It's pretty much unequivocally a meta-tag. $\endgroup$ Sep 18, 2015 at 7:21
  • $\begingroup$ @MartinSleziak Thanks for that. I'm not sure that people read the tag information all that carefully most of the time, which is why I was hesitant about noting this. But the excerpt should indicate to look at the wiki before posting. $\endgroup$ Sep 18, 2015 at 7:24
  • $\begingroup$ @NajibIdrissi It is certainly a meta tag. But many users on this site advocate special treatment for Project Euler questions. For this reason, I think it might be useful to have them marked in some way and tag is a simple way of doing this. This tag was discussed here. However, that post is from 2010 and it proposes also other, somewhat similar, tags. If there should be a discussion whether the tag should be completely removed, my opinion is that it would deserve a separate question. (IMO it is sufficiently different from the issues discussed here.) $\endgroup$ Sep 18, 2015 at 7:34
  • $\begingroup$ @MarkBennet If you think that the tag-excerpt should be improved in some way, I think you should go ahead and edit it. (IIRC MathJax works in tag excerpts, but markdown not, so it is probably not possible to put there a working link. But even without link it can be probably phrased in some reasonable way so that user who takes time to read the tag excerpt would know where to find more info. $\endgroup$ Sep 18, 2015 at 7:37
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    $\begingroup$ I never meta-tag I didn't like (as Will Rogers famously never said). $\endgroup$ Sep 18, 2015 at 9:21

I am confused why this was not proposed as an answer yet:

Allow the questions (with proper attribution), if and only if they request hints as answers.

This would, similarly to homework questions, help those who are actively working on a problem, but cannot find a solution. At the same time, it avoids verbatim answers.

I feel this would be a compromise all sides could live with.

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    $\begingroup$ Yes, this works great with homework problems. $\endgroup$
    – user147263
    Sep 16, 2015 at 13:14
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    $\begingroup$ From the downvotes I gather that was sarcasm? $\endgroup$
    – mafu
    Sep 16, 2015 at 14:31
  • $\begingroup$ A homework question may garner four answers with hints, but it only takes one answer that explicitly states the numerical solution to spoil the whole point. $\endgroup$
    – Wildcard
    Jan 10, 2017 at 4:25

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