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?
When I was a fifth grader we were required to memorize all prime numbers below 20.
Is This Prime?
61–70 of 139 posts
Re: Is This Prime?
#62Re: Is This Prime?
#63My prime number skills only go up to 47 because that's how high Number Munchers went.
I was too busy shooting more meat than I could carry back to the wagon, or fleeing low to escape the osprey.
Re: Is This Prime?
#64Here is a "theorem" I learned: every number up to 100 which looks prime, is prime, except 91. Does anyone recall its name?
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. 7×13=91 is the only composite number under 100 that isn't caught by these rules.
A trick for remembering that 91 is composite is that it's of the form x² - y² (specifically 10² - 3²), so it's (x+y)(x-y) or 13 * 7.
Re: Is This Prime?
#65Re: Is This Prime?
#66This is really cool! I made a very similar game a couple years ago: https://jew.ski/prime-time/
It's interesting to compare the game play and design. My game is written in Elm and open source if anyone is interested. This website has keyboard inputs (y or n) which is a good idea. My game only does click/touch inputs.
Re: Is This Prime?
#67I've spent a good week of straight hours on primes by now, the most fun thing I've come up with was this boring sieve.
https://github.com/alexlieberman/Prime-Numbers/blob/master/S...
Re: Is This Prime?
#68Love it. But if you are clicking an answer just as time is running out, you won't get to see your score (it starts a new game).
Re: Is This Prime?
#69Is 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 Recamán 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/Recamán%27s_sequence
> If tomorrow someone discovered a closed-form equation for the nth prime, how would mathematics/the world change?
Btw, that kind of exists. There's a formula that produces nothing but prime numbers. It basically encodes sieving, and it coincidentally uses every letter of the English alphabet.
https://en.wikipedia.org/wiki/Formula_for_primes#Formula_bas...
Re: Is This Prime?
#70Is 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 Recamán 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/Recamán%27s_sequence
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.
None is known. Can't be a polynomial.