- #1
Toftarn
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Problem 1
Prove that p^2 - 1, where p is a prime greater than 3, is evenly
divisible by 24.
p^2 - 1 can be written as (p+1)(p-1)
Since p is a prime, (p+1) and (p-1) must both be even numbers.
Since every third integer is divisible by 3, either (p+1) or (p-1) must be divisible by 3.
So, this gives us the prime factors, 2, 2 and 3. But to make the product (p+1)(p-1)
divisible by 24, we need another 2. What I'm wondering is where this last 2 comes from.
Problem 2
m = 2^p - 1
Prove that, if p is not a prime, then m will not be a prime.
If p is not a prime, then it can be written as the product of two numbers, a and b.
p = ab
Thus m = 2^(ab) - 1.
This is as far as I've come. My book says that 2^(ab) - 1 will always be evenly divisible
by 2^a - 1. How can you see this? I have tried to factor out 2^a - 1, but I can't figure out what the other factor would be.
Any help would be greatly appreciated.
Toftarn
Homework Statement
Prove that p^2 - 1, where p is a prime greater than 3, is evenly
divisible by 24.
Homework Equations
The Attempt at a Solution
p^2 - 1 can be written as (p+1)(p-1)
Since p is a prime, (p+1) and (p-1) must both be even numbers.
Since every third integer is divisible by 3, either (p+1) or (p-1) must be divisible by 3.
So, this gives us the prime factors, 2, 2 and 3. But to make the product (p+1)(p-1)
divisible by 24, we need another 2. What I'm wondering is where this last 2 comes from.
Problem 2
Homework Statement
m = 2^p - 1
Prove that, if p is not a prime, then m will not be a prime.
Homework Equations
The Attempt at a Solution
If p is not a prime, then it can be written as the product of two numbers, a and b.
p = ab
Thus m = 2^(ab) - 1.
This is as far as I've come. My book says that 2^(ab) - 1 will always be evenly divisible
by 2^a - 1. How can you see this? I have tried to factor out 2^a - 1, but I can't figure out what the other factor would be.
Any help would be greatly appreciated.
Toftarn