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        riddles >> hard >> pq-p-q prime?
        
(Message started by: cool_joh on Jul 19^th, 2008, 5:31pm)

Title: pq-p-q prime?
Post by cool_joh on Jul 19^th, 2008, 5:31pm

I have check some pairs of primes (p,q). I found that, in most cases, pq-p-q is prime.

What can you say about this? When is pq-p-q is prime? When is it composite?

Title: Re: pq-p-q prime?
Post by ThudanBlunder on Jul 19^th, 2008, 5:47pm

If this was difficult (or impossible) to prove in Medium (http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board=riddles_medium;action=display;num=1195867555;), putting it in Hard won't make it any easier. ::)

Title: Re: pq-p-q prime?
Post by cool_joh on Jul 20^th, 2008, 1:42am

Wow, it was a long time ago. I didn't remember posting it. Sorry, you can lock this, and I'll revive the old topic to continue the discussion.