[HN Gopher] Is This Prime?
___________________________________________________________________
Is This Prime?
Author : jordigh
Score : 77 points
Date : 2021-07-15 18:23 UTC (4 hours ago)
(HTM) web link (isthisprime.com)
(TXT) w3m dump (isthisprime.com)
| koolba wrote:
| I was expecting an Amazon product search / review site and was
| pleasantly surprised that it is in fact a math game.
| Kluny wrote:
| I love it, but the game doesn't work for me! No response when I
| click Yes or No, or using the keyboard y and n. Just the clock
| ticking down. Chrome Version 91.0.4472.114 (Official Build)
| (64-bit) on Windows 10 Enterprise.
| lalaithion wrote:
| This reminds me of my favorite in-person magic trick to do.
|
| First, memorize all the two-digit primes. 25 numbers isn't that
| hard to memorize.
|
| Then, tell someone "Oh, I can instantly tell whether a number is
| prime or not. Give me a number, I'll tell you whether it's
| prime."
|
| If they tell you a number between 1 and 100, use your memorized
| list. Otherwise, it's a game of cold reading; if they just
| generated a random string of many digits, there's a low chance
| that the number actually is prime. "21923847" is a keysmash, and
| it's almost certainly not prime, because the frequency of primes
| goes down as numbers get bigger. And most people will ask you a
| number, hear "no", and then go check the number's primality.
| Eventually, they'll look up a number in advance; that number is
| almost certainly prime.
| the_arun wrote:
| After 8 attempts, I ran into "Game Over". Was just thinking
| about the satisfaction for the author of this site. There is
| just enormous fun in saying - Game Over - to another human :)
| [deleted]
| float4 wrote:
| And then one day, somebody asks you calmly: "what about
| 2^31-1"? Better memorise the small Mersenne exponents as well!
|
| https://oeis.org/A000043
| Igelau wrote:
| Why do I feel like I'm solving someone else's CAPTCHA?
| __michaelg wrote:
| Finally a way to sort out candidates that's even cheaper than
| making them implement B-trees.
| HeavenFox wrote:
| When I was a fifth grader in China, we were required to memorize
| all prime numbers below 100.
|
| Curious if that is common in other countries?
| faeyanpiraat wrote:
| How is that useful?
| healthysurf wrote:
| Vast majority of my school experience wasn't useful
| Zababa wrote:
| I don't think that was a thing in France (at least where I went
| to school) but we often used them indirectly to simplify
| fractions, so all in all maybe we had to know all primes under
| 25 I think?
| antman wrote:
| I don't think so. Remember any other interesting numbers list
| you needed to memorize?
| tokamak-teapot wrote:
| I learned all the integers.
| munchbunny wrote:
| It isn't standard in the US, although at some point I memorized
| them to prepare for buzzer races in math competitions. It was
| in no way reflective of anything useful in real life, but it
| was fun.
|
| There were a few sets of common numbers, formulas, and mental
| calculation tricks that were useful to just always have in the
| back of your head. Perfect squares and cubes under 1000, powers
| of 2 and 3, prime numbers below 100, interior angles of regular
| polygons up to 10 sides, binomial coefficients, Pythagorean
| triples, factorials up to 9!, common roots out to 3-4 decimal
| places, and a few others that I've no longer needed for almost
| 20 years at this point.
| slmjkdbtl wrote:
| Would pay to for more chances
| ridiculous_fish wrote:
| Here is a "theorem" I learned: every number up to 100 which looks
| prime, is prime, except 91. Does anyone recall its name?
| tshaddox wrote:
| 49 looks prime to me. Another commentator says it doesn't count
| because it's a square number, but square numbers don't really
| have a particular "look" to me in the same way that 2-digit
| numbers ending in 5 or with digits summing to a multiple of 3
| do.
| nilstycho wrote:
| This is a great "theorem", thank you!
|
| It's easy to determine divisibility by 2, 3, 5, and 11. 72 is
| also easy because it's a square. 7x13=91 is the only composite
| number under 100 that isn't caught by these rules.
| bbx wrote:
| I agree. And I would add 51 to that.
| TheDong wrote:
| 51's an easy one because 5+1=6, and 6 is divisible by 3, so
| it must be divisible by 3.
|
| It's easy to try 'divisible by 5' (ends in 5 or 0) and
| 'divisible by 3' (sum of digits is divisible by 3). 91 isn't
| found as prime by those two tests, so it needs the extra
| exceptional rule.
| [deleted]
| jkingsbery wrote:
| I think it's called "The Ridiculous Fish Theorem."
|
| +1... I lost two games in a row, both times on 91.
| [deleted]
| gerbler wrote:
| I really like it.
|
| I wonder if the text could be dropped once it starts. I found
| myself reading it each time which ended up distracting me a
| little and sometimes I would rush and tapped the opposite of what
| I intended.
| davjhan wrote:
| I love these simple web games! Great idea. One way to improve it
| is to add some more juice when you answer a question. Right now,
| the text in the number just swaps to the next question, so any
| sort of small visual feedback will help first time players get it
| more.
|
| I also like to make these small web mini games on the side.
| Here's one where you guess the year that famous events happened:
| https://guess-the-year.davjhan.com/
| exo-pla-net wrote:
| Good practice for learning divisibility rules
| https://en.m.wikipedia.org/wiki/Divisibility_rule
| nonfamous wrote:
| I've always wondered: how feasible is it to implement an
| "isprime" function, via lookup table? If such methods are used,
| is cryptography getting weaker and weaker in practice as more
| large primes are discovered?
| jkingsbery wrote:
| Great game!
|
| Keyboard short cuts would make it a bit better.
| progval wrote:
| you can use left and right arrows
| mcintyre1994 wrote:
| The help text says y and n work, I'm on mobile and haven't
| tried though.
| hughdbrown wrote:
| Y and N for yes and no.
| whoomp12342 wrote:
| man, these tech screenings are getting out of control
| optimalsolver wrote:
| Is there a reason we're obsessed with primes beyond aesthetics?
| Why does this set of numbers garner all the headlines as opposed
| to some other arbitrary integer sequence like the Recaman numbers
| [0] ?
|
| If tomorrow someone discovered a closed-form equation for the nth
| prime, how would mathematics/the world change?
|
| [0] https://en.wikipedia.org/wiki/Recaman%27s_sequence
| johnday wrote:
| The prime numbers are critical in cryptography. Almost all of
| our current digital security infrastructure is based on the
| concept of multiplying large numbers together modulo suitably
| big prime numbers.
|
| Any major step towards understanding them (such as a closed-
| form equation for primes) would have major mathematical knock-
| on effects which may or may not undermine these methods, or
| provide us with a basis for even stronger cryptographic
| mechanisms to make use of in the future.
| Jtsummers wrote:
| Your original link 404'd on me (you seem to have replaced it
| with a different one though). Here's the working Wikipedia
| link:
|
| https://en.wikipedia.org/wiki/Recaman%27s_sequence
| optimalsolver wrote:
| Thanks. I've edited the link.
| X6S1x6Okd1st wrote:
| I'm not sure about a closed-form equation for the nth prime,
| but if integer factorization can be done in linear time then
| much of applied cryptography needs to be replaced.
| kstrauser wrote:
| 78. Who did better?
| X6S1x6Okd1st wrote:
| They've included 1 as not a prime. That was a fairly recent
| decision.
| drdec wrote:
| One is not a prime number. If you allow one to be a prime
| number, then you can no longer say that each natural number has
| a unique prime factorization.
|
| This makes the concept of prime numbers much more useful when
| one is excluded.
| Igelau wrote:
| > If you allow one to be a prime number, then you can no
| longer say that each natural number has a unique prime
| factorization.
|
| I don't dispute that, by definition, 1 is not prime, but I
| don't see how this statement would follow if we considered it
| prime.
|
| Edit: it seems more like it would be that every factorization
| would implicitly have 1^n tacked onto it, and while that
| isn't exactly useful, it doesn't break the game.
| Jtsummers wrote:
| It's not a recent decision. It's a (low grade) debate that's
| spanned thousands of years now.
| copperx wrote:
| Who's they? Is this a mathematical consensus?
| squeaky-clean wrote:
| "they" is the game developers of this game.
| sebzim4500 wrote:
| I'm not sure why but having 'yes' be on the left is really
| messing me up.
| bla3 wrote:
| You must be a macOS or iOS user.
___________________________________________________________________
(page generated 2021-07-15 23:01 UTC)