What is the symbol for summing odd numbers?

billym · #1 $Old$ November 5th, 2009, 04:13 PM

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

artvandalay11 · #2 $Old$ November 5th, 2009, 04:35 PM

Quote:

Originally Posted by billym $View Post$

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

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

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

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

$2r+n=k$

Jameson · #3 $Old$ November 5th, 2009, 04:36 PM

Quote:

Originally Posted by billym $View Post$

What would I use instead of $\sum$ 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.

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

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

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

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

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

Plato · #4 $Old$ November 5th, 2009, 04:51 PM

Quote:

Originally Posted by billym $View Post$

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

$\sum\limits_{j = \left\lfloor {\frac{n} {2}} \right\rfloor }^{\left\lfloor {\frac{{k - 1}} {2}} \right\rfloor } {2j + 1}$

harbottle · #5 $Old$ November 6th, 2009, 02:35 AM

edit:nevermind

billym · #6 $Old$ November 7th, 2009, 05:11 AM

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