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Nov 5, 2013 at 17:47 history edited GH from MO CC BY-SA 3.0
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Oct 31, 2013 at 13:54 vote accept Huichi Huang
Oct 31, 2013 at 13:30 comment added Huichi Huang @GH:Thanks.Nice proof. One more comment: the procedure to produce infinitely many $N$ seems to go as follows: suppose we have $N_1,\,...\,N_i$ as required, then let $M=N_1\timesN_2...\timesN_i$, then we get $N_{i+1}$ satisfying with the required properties but distinct from $N_1,...,N_i$.
Oct 31, 2013 at 12:33 comment added GH from MO @fedja: I love your version, it is great! Can you also give infinitely many pairwise coprime $N$'s without Dirichlet?
Oct 31, 2013 at 12:29 history edited GH from MO CC BY-SA 3.0
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Oct 31, 2013 at 10:54 comment added fedja Lovely. So, all we need is $k$, and a large $N|p^k-q$ with $k$ relatively prime to $\varphi(N)$. That $N$ or $k$ is prime is of no importance really. Let's do it avoiding Dirichlet. The primality of $k$ and the condition $p<q$ are ingenious, so we keep them. Take a huge prime $k>q-p$. Then $p^k-q\equiv p-q\mod k$. Now take the prime factorization of $p^k-q$ and remove all prime factors that are $1$ modulo $k$. Let $N$ be what is left. Then $k\not\mid\varphi(N)$ ($k$ is neither a prime in $N$, nor a divisor of a prime in $N$ minus $1$) and we still have $N\equiv p-q\mod k$, so $N\ge k+p-q$.
S Oct 31, 2013 at 10:17 history suggested Michael Zieve CC BY-SA 3.0
Minor edits for clarity.
Oct 31, 2013 at 9:42 review Suggested edits
S Oct 31, 2013 at 10:17
Oct 31, 2013 at 8:31 history edited GH from MO CC BY-SA 3.0
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Oct 31, 2013 at 8:24 history edited GH from MO CC BY-SA 3.0
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Oct 31, 2013 at 6:08 history edited GH from MO CC BY-SA 3.0
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Oct 31, 2013 at 5:57 history edited GH from MO CC BY-SA 3.0
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Oct 31, 2013 at 5:42 history undeleted GH from MO
Oct 31, 2013 at 5:42 history edited GH from MO CC BY-SA 3.0
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Oct 30, 2013 at 18:18 history deleted GH from MO via Vote
Oct 30, 2013 at 16:32 comment added Will Sawin How does this produce infinitely many $N$? What if they all divide $p-q$?
Oct 30, 2013 at 16:17 history edited GH from MO CC BY-SA 3.0
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Oct 30, 2013 at 15:37 history edited GH from MO CC BY-SA 3.0
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Oct 30, 2013 at 15:25 history edited GH from MO CC BY-SA 3.0
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Oct 30, 2013 at 15:20 history answered GH from MO CC BY-SA 3.0