Sunday, 7 July 2013

prime numbers - If qmid2p+3p then qgtp





Let p,q positive prime numbers, q>5. Prove that if
q(2p+3p) then q>p.







First, it's clear that pq because, using Fermat's little theorem, 2p=2modp and 3p=3modp, therefore 5=0modp false because q>5.



Now suppose q<p. I tried to analyse 2p+3pmodq but I didn't get a contradiction.



Answer



HINT:



For p>2



(32)p1(modq)



ordq(3/2)|(p,q1)



But As p is prime, ordq(3/2)=1 or p




ordq(3/2)=132(modq)50q|5q=5



Else p|(q1)


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