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MathGroup Archive 2000

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Re: Selecting numbers with all odd digits

  • To: mathgroup at smc.vnet.net
  • Subject: [mg22199] Re: [mg22170] Selecting numbers with all odd digits
  • From: Andrzej Kozlowski <andrzej at platon.c.u-tokyo.ac.jp>
  • Date: Fri, 18 Feb 2000 02:34:35 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

on 00.2.17 3:23 PM, Tom De Vries at tdevries at shop.westworld.ca wrote:

> Hello all,
> 
> In one of the math classes I am teaching we are doing some work with
> permutations and combinations.  One question in the text was,  "how many
> positive integers less than 700 have all odd digits?"
> 
> I had done the question "by hand" and then wondered how to use Mathematica
> to demonstrate that the solution was the correct one.
> 
> I am still very far down on the learning curve in most things, but I managed
> to bludgeon my way to an answer  (thankfully the same as mine!)
> 
> Select[
> 
> Range[699],
> 
> Union[ OddQ [ IntegerDigits[#]]] == {True} &
> 
> ]
> 
> I am sure my trial and error method can be improved upon.  I am not talking
> speed as much as simply using Mathematica in a way that makes sense and
> would be more logical??
> 
> Thanks for any suggestions might have!
> 
> Tom De Vries
> Edmonton, Alberta
> Canada
> 
> 

Your code is basically fine. The following seems to me just a little bit
more natural and also somewhat faster:


In[5]:=
Select[ Range[10^5], And @@ OddQ [ IntegerDigits[#]] == True & ]; // Timing
Out[5]=
{13.7167 Second, Null}
In[6]:=
Select[Range[10^5], Union[ OddQ [ IntegerDigits[#]]] == {True} & ]; //
Timing
Out[6]=
{23.7 Second, Null}

--
Andrzej Kozlowski
Toyama International University
Toyama, Japan
http://sigma.tuins.ac.jp/




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