# Homework Help: Perfect Number Proof

1. Nov 30, 2013

### srfriggen

1. The problem statement, all variables and given/known data

Prove: If 2p-1 is prime, then 2p-1(2p-1) is a perfect number.

2. Relevant equations

I am simply having trouble understanding one part of the end of the proof, namely:

Why does $\sigma$(2p-1)=2p-1 ?

The proof I'm working off of (trying to understand is on page 4 of this link: http://www.math.dartmouth.edu/~jvoight/notes/perfelem.pdf

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 30, 2013

### Dick

It's pretty easy. The divisors of 2^(p-1) are 1,2,2^2,2^3,...2^(p-1). The divisors form a geometric series. What's its sum?

3. Nov 30, 2013

### srfriggen

aha, thanks!

4. Nov 30, 2013

### Dick

Yeah, and actually this is already mentioned in the paper in Theorem 4.

5. Nov 30, 2013

### srfriggen

oh man I can't believe I missed that :uhh:

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