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## #1 2005-05-17 00:50:14

w0lfman
Novice

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### Factorials

Well, I know what factorials are, it is n*(n-1)*(n-2), etc. until you've gone all the way down to zero. What i'm looking for is a way to express n+(n-1)+(n-2), etc. Do you know of any way to write this?

Thanks, w0lfman

## #2 2005-05-17 03:16:45

Zach
Super Member

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### Re: Factorials

3n-3, I expect. I may be wrong.

Boy let me tell you what:
I bet you didn't know it, but I'm a fiddle player too.
And if you'd care to take a dare, I'll make a bet with you.

## #3 2005-05-17 04:42:29

mathsyperson
Guest

### Re: Factorials

(I think) this topic's been done before, but anyway...

You are asking how to express Triangular Numbers.

You can do this by using this formula:    n(n+1)
---------
2

or also 0.5n² + 0.5n.

## #4 2005-05-17 07:50:15

MathsIsFun

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### Re: Factorials

Yep, just recently covered here.

The question was adding up the numbers 1,2,3,4,5 (your problem is just like 5,4,3,2,1) but my answer included being able to add things like 5,6,7,8,9 (ie the general solution) ... and Milos rounded out the whole discussion.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman