# Thread: need help with these congruence and other problems for number theory

1. ## need help with these congruence and other problems for number theory

1) If k > 2, and n = 2k-3, show that 3n is not congruent to 1 (mod 2k).
2) Let p > 3 be a prime, and suppose that p º 3 (mod 4). If q = 2p+1 is also prime show that 2p -1 is never prime.
3) Let p be a prime ¹ 2 or 5, and let N be any integer. If p | (N2-5) show that p is of the form 1+5k, or 4+5k
4) Let p be a prime. Show that every prime divisor of 2p -1 is > p.

2. ## Re: need help with these congruence and other problems for number theory

Originally Posted by henderson7878
1) If k > 2, and n = 2k-3, show that 3n is not congruent to 1 (mod 2k).
2) Let p > 3 be a prime, and suppose that p º 3 (mod 4). If q = 2p+1 is also prime show that 2p -1 is never prime.
3) Let p be a prime ¹ 2 or 5, and let N be any integer. If p | (N2-5) show that p is of the form 1+5k, or 4+5k
4) Let p be a prime. Show that every prime divisor of 2p -1 is > p.
And what have you been able to do so far?

And for the sake of clarity, please do not post so many questions in one thread.

-Dan