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    [–] Tag for college math that has riddles that may use more advanced theorems? HarryPotter5777 2 points ago in mathriddles

    Nope, not currently (which, given the usual state of affairs in Reddit, means "we might get this feature in a decade if the admins haven't taken away the whole tagging system in the first place").

    Don't worry about posting things that require more high-level background, though if the problem is elementary and the solution requires a decently high-powered theorem it's probably worth stating as such in the post.

    [–] I'm an amateur, 14 year old mathematician. I've been working on something for a while, and I thought that some of you might find it interesting. HarryPotter5777 1 points ago in math

    Strongly, strongly seconded.

    I first attended Mathcamp when I was 14, and came back again the next year. And again. And again. (And again, if I come back as a counselor next summer.) The math is phenomenal, of course, but it's also the most wonderful social environment I've ever been in - some of the best and closest friendships I've ever had originated there, and those 4 Julys have been the best months of my life. If you're considering applying (the qualifying quiz should come out around New Year's!) and have any questions about camp, feel free to send me a PM :)

    [–] Tag for college math that has riddles that may use more advanced theorems? HarryPotter5777 5 points ago in mathriddles

    Is there something you'd want to achieve with this sort of tag that just putting a note to that effect in the post wouldn't accomplish? We'd still want difficulty rankings and solved/unsolved status, so having an "advanced math" tag means having 6 more tags total, and the subreddit is far from large enough to need or handle splitting in two.

    I guess I'm not sure what you'd like to do with this distinction, and so I'm not sure what the best way is to work toward that goal outside of adding lots of tags or a new sub (neither of which are likely to work well).

    [–] [Let's Reread] Questionable Content (“The Weirdest Eschaton”, Comics #390 - #399) HarryPotter5777 3 points ago in questionablecontent

    Man, I really like some of the dialog around this era of QC. I've adapted loads of it for my own conversations and notice myself near-quoting characters from around this time period all the time. Anyone else?

    [–] Where Would You Recommend a New Reader Start? HarryPotter5777 3 points ago in questionablecontent

    For those looking for a link, that's comic 1800 (or a bit later if you want to skip post-breakup drama).

    [–] Prime series HarryPotter5777 1 points ago in mathriddles

    Please flair your post! (Or, if you're on mobile, let me know and I can set it for you.)

    Yes, by induction. We first have {2}, then {2,3}. {2,3,5} isn't immediately possible, so we add multiples of 2*3 until it is. By CRT, it will be eventually. Once we have {2,3,5} somewhere (in this case at indices 8-10), add 30 until the next one is a multiple of 7 (so a158, a159, a160, a161). Iterate forever. At each portion of the sequence not determined by such a procedure, choose the ais arbitrarily.

    [–] Just took the time to look at Jeph's Twitter Account... HarryPotter5777 18 points ago in questionablecontent

    I mean, yes, fuck those people. But I prefer a world where some people who deserve to get punched stay safe to a world where "people getting assaulted on the streets for their opinions" is a thing that happens, regardless of how repulsive said opinions are. "Be kind to other except when they're really really bad, because then seriously fuck those people" is not a norm that a peaceful society can function under, because there are other people who are going to hate you as much as you hate Nazis and your moral system should not work conditional on your faction having strength in numbers. The legal system in the US is flawed in many ways and doesn't always accomplish everything we might want it to, but there are really good reasons why we have it instead of vigilante justice.

    [–] Just took the time to look at Jeph's Twitter Account... HarryPotter5777 22 points ago in questionablecontent

    Neither do I! All of the white supremacists in that rally are horrible people and I would be happy if they all spontaneously combusted right now. I just don't think that a societal norm of punching anyone you deem a Nazi is effective at accomplishing anyone's goals.

    [–] Just took the time to look at Jeph's Twitter Account... HarryPotter5777 22 points ago in questionablecontent

    I'm not remotely close to conservative (I'd be surprised if I vote anything other than the democratic candidate for as long as the current political parties exist), and Trump is a horrible president on so many levels.

    I just think that "give spontaneous vigilante justice to people we ideologically disagree with" is a pretty horrible paradigm and that most people on Jeph's side of things are far too quick to advocate both nazi-punching and nazi-categorizing in ways that are unproductive for anyone.

    [–] Just took the time to look at Jeph's Twitter Account... HarryPotter5777 11 points ago in questionablecontent

    Yeah, agreed - he writes an excellent comic full of thoughtful and caring characters that I like reading, but IRL he seems to split the world into "reasonable liberal people" and "literal nazis and the equally-detestable people who refuse to punch them" with nothing in between.

    [–] The Weird Dichotomy of Sentience and Ownership in QC HarryPotter5777 4 points ago in questionablecontent

    I think this stuff is super interesting, and I'd love to see it explored more - my personal preferred resolution to this is basically just a hardcore retconning of a lot of early QC's stuff here to basically set robots on equal footing with humans.

    [–] Selection function HarryPotter5777 2 points ago in mathriddles

    Choose the smallest element of X, unless X contains the minimal-absolute-value difference between its length and the nearest power of 2, in which case choose that. Then f satisfies the first condition by construction, and the second by appending k and arbitrary additional integers to X until the length is 2j+k for sufficiently large j.

    Edit: A better solution


    [–] Weighing sets of balls HarryPotter5777 3 points ago in mathriddles

    We may assume that all weighings balance, since if they ever fail to do so we will have a valid weighing. Weigh A against B, then AB against CD, etc., until we have 32 of the same weight - then these 32 and the other 32 have different weights. This takes 5 weighings - I haven't proved it's minimal yet, but it seems relatively easy to do so.

    [–] Numbers whose digits squared sum to a perfect square HarryPotter5777 2 points ago * (lasted edited 10 days ago) in mathriddles

    Take the k2-digit number 111...111. We reduce 1111->4 and 11...1->9, reducing the length by 3 and 8 respectively. Sums of 3s and 8s can form any number larger than 3*8-3-8=13. Such a sum with a 3s and b 8s uses 4a+9b 1s, so we will have used up at most 4/3 times our reduction in the digit length. Thus, we can subtract anything greater than 13 and less than 3k2/4. If we solve the quadratic


    we find that k≥6 suffices to create a cascade in which any number missed by taking away values from k2 is covered by k+1, which is turn is covered by k+2, etc. Since n2/4 is increasing this obtains all integers greater than or equal to 62/4=9. For the remaining:








    Thus good numbers exist in all bases ≥5, and in base 4 with the exception of 2 digits.

    [–] Find a function HarryPotter5777 1 points ago in mathriddles

    From the sidebar:

    Codebreaking and "guess the rule" type posts are not permitted; if you wish to submit such a post, do so on subreddits such as /r/puzzles.

    As such, your post has been removed.

    [–] [2017-05-22] Challenge #316 [Easy] Knight's Metric HarryPotter5777 1 points ago in dailyprogrammer

    Thanks! Intermittently for 5 years or so, but just very basic stuff (Khan Academy's ProcessingJS platform); I haven't put much real effort into learning new things until the last 2 years.

    [–] Convex polytope HarryPotter5777 2 points ago in mathriddles

    Here's a non-overkilled solution, explained a little poorly because high-dimensional stuff is hard:

    (Intuition-wise, you should be analogizing to the happy ending problem here - it's the same proof.)

    Take the convex hull of all the points. This is a d-dimensional polytope, so it has to have at least as many vertices as the d-simplex, i.e. d+1. Either we've got ≥d+2 vertices in our set, in which case we're done, or we have exactly d+1, in which case the 2 remaining points (call them P, Q) lie inside our convex hull. Consider the line PQ; by our non-colinearity assumption and the convexity of the simplicial convex hull, it intersects at most 2 facets. Since the d-simplex has d+1 facets (one opposite each vertex), it follows that for all d≥2, we can find some vertex to eliminate such that the remaining d points of the convex hull form a facet not intersected by PQ. This means that the d-simplices formed by the facet and one of P,Q do not contain the other point, so the convex hull of all d+2 points can't include just one of P, Q. Therefore, it includes both of them, and has the desired p+2 points on it.

    [–] Here's a good one HarryPotter5777 1 points ago in mathriddles

    This is not even remotely math-related, and violates our rules on titles. As such, your post has been removed. Please consult the sidebar before posting in the future.

    [–] Faye is nothing but a Mary Sue HarryPotter5777 34 points ago in questionablecontent

    Um, her dad shot himself in front of her? I don't think that counts as a long-term plus in anyone's book.