Jump to content
Obscure_Trash

> How high can you count before a mod posts?

Recommended Posts

Yeah, it's hot where I am.  I've got air conditioning, though, so lucky me.  The weather pattern here right now actually has clear mornings that start tolerable and get hot, and then it often rains in the afternoons.  Yesterday was a spectacular example, though, and then I went out in it to check on something.

 

16

Share this post


Link to post

31 is prime again.

 

Actually, that's a pretty good formula for a new pair of prime numbers.  You take all the consecutive primes starting from 2 going up to... whenever, and then you multiply them all together, and then you add or subtract 1.

 

So 2x3x5 = 30.  29 and 31 aren't divisible by anything, because 2, 3, and 5 have been ruled out (it's right next to a multiple of each of them) and all the other options are too big.  It doesn't get all of the prime numbers, but if you just need a prime number, it works.

 

It gets unwieldy pretty fast, though.  2x3x5x7 = 210, and then multiply that by 11 and you get 2310.  That times 13 is 30030.  So I can tell you 30029 is prime, but it'll be a pain in the neck to prove.  Try multiplying 30030 by, uh, 17, 19, 23, and 29.  C'mon, do it!  It'll be fun!

Share this post


Link to post