# Thread: What is the symbol for summing odd numbers?

1. ## What is the symbol for summing odd numbers?

What would I use instead of $\displaystyle \sum$ if I just wanted to sum odd values for some number n through k?

2. Originally Posted by billym
What would I use instead of $\displaystyle \sum$ if I just wanted to sum odd values for some number n through k?

$\displaystyle \sum_{i=0}^r 2i+n$

Where $\displaystyle n$ is the odd number you want to start with

You would need to decide what $\displaystyle r$ would be so that you stopped at the correct value

$\displaystyle 2r+n=k$

3. Originally Posted by billym
What would I use instead of $\displaystyle \sum$ if I just wanted to sum odd values for some number n through k?
I think you mean start from n and end at k by 2's. You can do this a few ways.

$\displaystyle \sum_{n=1,3,5...}^{k} a_n$ works but looks bad.

If you want to sum over all odds you can write $\displaystyle \sum_{odds}$

If you want to skip terms in a sequence you can write

$\displaystyle \sum_{n}^{k} a_{2n}$

I don't know exactly what you meant but those are some of my guesses.

4. Originally Posted by billym
What would I use instead of $\displaystyle \sum$ if I just wanted to sum odd values for some number n through k?
$\displaystyle \sum\limits_{j = \left\lfloor {\frac{n} {2}} \right\rfloor }^{\left\lfloor {\frac{{k - 1}} {2}} \right\rfloor } {2j + 1}$

5. edit:nevermind

6. I think I'll go with Jameson's bad looking one. Does the job.