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[PTTG??]

(n)+(n-1)+(n-2)+... (n-n)

I know there is a name and perhaps a symbol for that function. What is it?
If the utterly worthless n*(n-1)*(n-2)*...(n-n) has something as simple as ! to express it, what expresses the nice georgia-fonted equation up there? It couldn't possibly be "?", could it?

[Osmosis Jones]

That would be represented by capital sigma.. Specifically, that series would be expressed as

Code: [Select]

  n
---
\    (n-i)
/
---
 i = 0


[Twiggie]

plus, n! isnt unimportant. its very helpful in combinations and permutations

[bjlong]

Or, equivalently,

Code: [Select]

  n
---
\    (i)
/
---
 i = 0


[PTTG??]

I sure do know where to go for math help.
The american education system is pretty much post-apocalyptic.

[Alexhans]

plus, n! isnt unimportant. its very helpful in combinations and permutations

VERY Important...  Factorial is awesome for probability.

Don't dare minimize it! 

[bjlong]

Well, these aren't exactly ubiquitous functions--most people will never need to know the notation--so you not knowing them from public school is fine if you've just taken algebra and geometry. By pre-cal, you really should know summation notation, though.

[Osmosis Jones]

...and if you go to uni, you should really know Einstein summation notation (it's basically a way of getting rid of the sigma in favour of subscripts).

[Techhead]

As bjlong noted, your series basically comes out to n+(n-1)... +3+2+1+0, which is equivalent to the series 1+2+3 ... (n-1)+n.
They're called triangular numbers.
Because they make triangles.

Code: [Select]

                      *
             *       * *
      *     * *     * * *
 *   * *   * * *   * * * *They can be expressed as an easy quadratic equation.
T(n) = (n^2 + n)/2
Also, its nC2.
There's useful stuff you can do with it, which you can see after clicking this link.
It's the solution to the handshake problem, and the sum of two consecutive triangular numbers is a square number. Its also the third diagonal column in Pascals triangle.

I hope I answered your question.

[Maggarg - Eater of chicke]

I can tell you about the motivation and ideals of the American revolutionaries (i.e We don't want to pay no british taxes. Less than a damn shilling.) but not maths.

[Techhead]

I can tell you about the motivation and ideals of the American revolutionaries (i.e We don't want to pay no british taxes. Less than a damn shilling.) but not maths.

Hey! I'm an American and I think I answered the question the best of anyone here.

[Alexhans]

Hey! I'm an American and I think I answered the question the best of anyone here.

I know there is a name and perhaps a symbol for that function. What is it?

Actually... he did:

Or, equivalently,

Code: [Select]

  n
---
\    (i)
/
---
 i = 0


You just developed on what it was about and what uses did it have, wich was really interesting...
 

[zchris13]

Which is no less a correct answer than the other dude gave.

[bjlong]

I'm an American also.

[Deon]

Let's start a thread "who is american"?

I am russian . Shoot me in da face.

Also, since nowadays it's popular to link to the most useful and useless at the same time e-resource: wikipedia, eat this:
http://en.wikipedia.org/wiki/Summation

How did it end up in Creative projects? Let us start a thread on factorial, dividing, multiplying and substracting, let alone probability operators.