Can someone help me with how to go about this problem? Find all primes p such that: 8p^2 + 1 is also a prime, Thanks -Kate
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Originally Posted by katie07 Can someone help me with how to go about this problem? Find all primes p such that: 8p^2 + 1 is also a prime, Thanks -Kate If p is odd then p = 1(mod 3) or p = 2(mod 3) in either case p^2=1(mod 3) so 8p^2+1 is always divisible by 3.
Originally Posted by ThePerfectHacker If p is odd then p = 1(mod 3) or p = 2(mod 3) in either case p^2=1(mod 3) so 8p^2+1 is always divisible by 3. So you leave the possibilities p=2 or p=3. Now for p=2 8p^2+1 = 33 which is not prime. For p=3 8p^2+1 = 73 which is prime. RonL
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