4 ms·
To make the entrants feel smarter. The whole thing is, of course, completely isomorphic to a guess-an-integer competition, but the rather minimal effort you nee
by planetguy 14y ago
To make the entrants feel smarter. The whole thing is, of course, completely isomorphic to a guess-an-integer competition, but the rather minimal effort you need to go to to figure out the Nth prime makes it all worthwhile.
Perhaps it also indicates something about which primes sound primest, though. 29 is an outlying underachiever, suggesting that "29" doesn't spring to mind when you ask someone to name a prime... certainly I had to think for a moment to make sure it really was a prime. 23, 17, 37 are overachievers -- these are really prime-sounding primes, no doubt about it.
- robinsloan 14y agoAuthor here: I am also fascinated by this sense of certain numbers sounding prime (or more prime than others). For instance -- maybe this is just me -- I think 109 (the first winner) doesn't sound prime at all. But 17! Yes! It can't shut up about how prime it is!
- parfe 14y agoDid you receive any emails choosing composite numbers? To me, 51 sounds prime.
- robinsloan 14y agoYes, many! On the submission form, I even referred folks to Wikipedia's list of prime numbers but, alas.
- baddox 14y agoA number is divisible by 3 if the sum of its digits is divisible by 3.
- deleted 14y ago[deleted]
- PieSquared 14y agoA number theory class I once took provided us with the following "proof", claiming, in fact, that it was the most useful thing we would learn, and would make a great party trick. Theorem: Anything less than 91 which looks prime is prime. Proof: To do this, we will calculate the smallest number that looks prime but isn't. The numbers 2, 3, 4, 5, and 6 all have easy and quick divisibility rules, so our number cannot be divisible by any of them. 7, however, is hard to check for - so clearly the first number that looks prime but isn't will be divisible by 7. Sadly, everyone realizes 49 isn't prime, because it's a square, so we need to find the next difficult prime factor. 8, 9, 10, 11, and 12 are all also subject to quick tests and divisibility rules, so discount those. 13, however, is ugly - thus, the first number that looks prime but isn't is 7 times 13, which equals 91. Q.E.D. (My professor insisted this stood for "Quite Easily Done".)
- SoftwareMaven 14y agoIsn't this just the inverse of memorizing multiplication tables?
- taftster 14y agoRight. And numbers like 117 and 119 secretly trick (at least) me into thinking they are prime.