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## #1 Re: Help Me ! » combination number... » 2012-11-12 12:05:54

I get it now. Thanks for explaining!

## #2 Re: Help Me ! » combination number... » 2012-11-11 12:01:04

Blitz wrote:

So here's the same question : Can you explain your example please, because I don't see how {4,7,9,10,11} results in your algorithm. I don't see the link between 4,7,9,10,11 and the numbers in your algorithm:

Thx for clarifying the second question.

## #3 Re: Help Me ! » combination number... » 2012-11-09 10:32:43

bobbym wrote:

A couple of questions, usually formulas are given for permutations.

Do you want {1,2,3,4,5} to be different than {5,4,3,2,1}?]

No, so I think we're talking about combinations here.

and how do you write

as a plain formula?

## #4 Help Me ! » combination number... » 2012-11-07 11:25:20

Blitz
Replies: 7

Hi,

I`ve carefully read this site's in depth explanation regarding combinations and permutations and I`ve learned a lot.

However... I have two questions:

1. I am still searching a formula that can give me the RANKING POSITION of a combination. I`ll give an example:

lottery numbers : 5 numbers are chosen from 50 numbers. this gives 2118760 possible combinations, from 1-2-3-4-5 to 46-47-48-49-50.
Now I need a formula that gives me the ranking position (from 1 to 2118760), when I enter the 5 chosen numbers in the formula. For example, combination 1-2-3-4-6 should return ranking position #2, combination 1-2-3-4-7 should return 3, and so on.

What is the formula for this?

2. I have noticed that the Combinations and Permutations Calculator on this site calculates the result at any keystroke. This makes me believe it uses a non-recursive factorial function. So far, I haven't found any non-recursive factorial math function (to use in visual basic for example). I have used a recursive factorial function so far, but when the number of possible combinations gets too high, I get -an expected- stack overflow. What function does this website use?