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Prime number of length k.

Callan
Post Icon Posted: Submitted by Callan on 17 September 2009 - 12:58am.

Joined: 2008-09-30
Posts: 173

Hey,
I was just wondering if there was any result which shows you can always find a prime of length k for any k. From the prime number theorem its clear that if you randomly (with a uniform distribution) select numbers of length k then after a given number of selections you can estimate the probability of finding a prime (and so show that there is a high likelihood of finding primes of length k). I don't really know enough number theory so this may be a pretty trivial problem. (Also I'm pretty sure I was reading something about this recently but can't remember where, any ideas?)
Thanks.

Callan
Post Icon Posted: 17 September 2009 - 12:03pm

Joined: 2008-09-30
Posts: 173

ok, this is what I was looking at: http://michaelnielsen.org/polymath1/index.php?title=Finding_primes but its about finding a polynomial time deterministic algorithm for a prime of at least length k.

cosmin
Post Icon Posted: 17 September 2009 - 2:49pm

Joined: 2006-11-02
Posts: 1291

Yeah, it's always possible. You can use Bertrand's postulate for example: there's always a prime between $ 10^k $ and $ 2\cdot 10^k $. I can't really think of anything more elementary, I doubt you can really find much easier because in essence both this and Bertrand's postulate say more or less the same thing.

Callan
Post Icon Posted: 17 September 2009 - 3:10pm

Joined: 2008-09-30
Posts: 173

Thanks, I think I'll go and check that out in 'Proofs from the Book'.