What is the last non zero digit of $100!$?

Is there a method to do the same for $n!$?

All I know is that we can find the number of zeroes at the end using a certain formula.However I guess that's of no use over here.

  • 1
    $\begingroup$ See here for a general formula. Or just do a search for "last non zero digit of n!" in this site, or look at the related links in to the right. $\endgroup$ – Calvin Lin May 18 '13 at 17:14

This question gets asked fairly frequently. There was originally a problem on the AMC asking for the last two digits. Here is my post on the single digit case, which is not all that much simpler than the two digit case.

  • $\begingroup$ I'm sure that this question has been asked before 2010 (year of the AMC question). $\endgroup$ – Calvin Lin May 18 '13 at 17:24
  • $\begingroup$ Oops, didn't check the date on that. For some reason, I had remembered it to be a lot earlier than 2010. $\endgroup$ – Jon Claus May 18 '13 at 17:48

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