🚀 go-pugleaf

In <4fr8be$ass@news.iconn.net>, thecrow@iconn.net (The Crow) writes:
>Here is what I am trying to do, I want to find the last NON-ZERO digit of a 
>given factorial.  For instance,
>
>5! = 120
>
>so the last non-zero digit is 2.  I want to be able to do this up to 1000.  
>Problem is, no matter how huge of a data-type you use, there isn't any way for 
>the computer to handle 1000!, it is however possible to find the last non-zero 
>digit somehow.  One thing I have tried is as I went through mulitplying the 
>series of numbers in the factorial (5 * 4 * 3 * 2) I would remove all the 
>trailing ZEROS, I got this to work up to 789, but it wont work with 1000 and i 
>am not really sure why.  If anyone has a clue how I can do this let me know.
>
>-- 
>The Crow - thecrow@iconn.net
>"It can't rain all the time"
>-Kryptology
>

You will get a zero at the end for every factor of 5 in the number:
2's are available in abundance. 
So: nzeroes:=0;
    for i:=1 to n
    do begin
         nfives:={factor i, not too hard, and get the exponent of 5.}
         nzeroes:=nzeroes+nfives;
       end;


Henk.

-----This is an airconditioned room, do not open Windows.-----
Henk Huisman                         h.huisman@wbmt.tudelft.nl
Systems and Control Group            Mekelweg 2
Delft University of Technology       NL-2628 CD Delft
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