# Thread: Trying to understand sigma functions

1. ## Trying to understand sigma functions

Hi math forum folks!

I'm trying to understand sigma functions in the context of a homework question that I have. I attached an image of the question in this post. The issue that I'm facing with 12c is that I got the wrong answer. To my understanding f(12) does not equal f(3) x f(4) - which is contrary to the textbook answer. I would like some clarification on why they equal each other (or if the textbook is wrong).

Additionally, I would like to understand 12d. better. The textbook said that two sigma functions would equal another "whenever a and b have no common factors other than 1", which I don't really understand why this would be the case.

I hope that someone can help me out!!!

- Olivia

2. ## Re: Trying to understand sigma functions

$f(12) = 1 + 2 + 3 + 4 + 6 + 12 = 28$

$f(3) = 1 + 3 = 4$

$f(4) = 1 + 2 + 4 = 7$

so ... $f(3) \cdot f(4) = 28$

I'll have to think about 12d.