wraithx on Sun, 26 Jun 2016 07:19:08 +0200

 Re: Need permutation help for n!/(n-r)!

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On 6/25/2016 7:53 AM, chandra sekaran wrote:
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```Hi Bill

I have not put the question properly.

(18:08) gp > 50!/(50-3)!
%3 = 117600

Out of 117600 ,  some number following permutation will fall. I want to find the
number.
[38, 40, 41] , [2,3,5], [10,11,12], [12,11,10]
or Find the three number permutation which will fall on 2000.

If  n grows bigger( say 600! ) fast finding three number set and reverse  is
possible?

Thanks

Chandrasekaran B

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You will need to define what order you want to put these elements in. For example [2,3,5], could be obtained with:
```[1,2,3] #1
[1,2,4] #2
[1,3,4] #3
[2,3,4] #4
[1,2,5] #5
[1,3,5] #6
[1,4,5] #7
[2,3,5] #8 *Found
Found on the 8th element.

Or, is it:
[1,2,(3-50)] #1-48
[1,3,(4-50)] #49-95
[1,4,(5-50)] #96-141
...
[1,49,50] #1176
[2,3,4] #1177
[2,3,5] #1178 *Found
Found on the 1178th element.

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Also, do the elements of interest for you range from 0-49, or from 1-50? (the above examples use 1-50)
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-David C.

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