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Re: count zeros in a number

  • To: mathgroup at smc.vnet.net
  • Subject: [mg121826] Re: count zeros in a number
  • From: Stefan Salanski <wutchamacallit27 at gmail.com>
  • Date: Tue, 4 Oct 2011 01:31:26 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <j69104$rda$1@smc.vnet.net>

On Oct 2, 2:40 am, dimitris <dimmec... at yahoo.com> wrote:
> Hello.
>
> Consider e.g. the number 24^24*55^55.
> This number ends with exactly 55 zeros as the following demonstrate
>
> In[201]:= Mod[24^24*55^55, 10^55]
> Mod[24^24*55^55, 10^56]
>
> Out[201]= 0
> Out[202]= 20000000000000000000000000000000000000000000000000000000
>
> What I want now is a way to count the zeros that a number ends without
> knowing in advance this number of zeros like in the above example.
>
> Thanks in advance.
> Dimitris

All these solutions are very interesting, and they all work, but I
believe the simplest solution is actually a built in function,
specifically: IntegerExponent[].
IntegerExponent[n,b] returns the highest power of b which divides n,
which for b=10, is the number of trailing zeroes of n.
moreover, the default value of b is already 10, so that
IntegerExponent[n] gives the number of trailing zeroes of n.
In[1]:= IntegerExponent[24^24*55^55]
Out[1]= 55
http://reference.wolfram.com/mathematica/ref/IntegerExponent.html

-Stefan Salanski



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