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MathGroup Archive 2006

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Re: Friedman Number

  • To: mathgroup at smc.vnet.net
  • Subject: [mg71613] Re: Friedman Number
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Sat, 25 Nov 2006 05:36:50 -0500 (EST)
  • Organization: The Open University, Milton Keynes, UK
  • References: <ejuqp4$i10$1@smc.vnet.net>

zeta wrote:
> Hi,
> 
> How progamming Friedman Number in Mathematica-Code
> 
> 
> Many Thanks
> Zeta
> 

[ Note: This is the 2nd attempt to post this reply to Mathgroup. ]


I followed the algorithm [1] for b == 10 and 2-digit numbers. I leave it 
to you to clean the code, catch some possible division by zero, and to 
extend the program to 3-digit numbers and above.

In[1]:=
values = Range[-1, 10];
pairs = DeleteCases[Flatten[Outer[List, values,
       values], 1], {0, _}];
possibles = Select[pairs,
     10*#1[[1]] + #1[[2]] == #1[[1]]*#1[[2]] ||
       10*#1[[1]] + #1[[2]] == #1[[1]]^#1[[2]] ||
       10*#1[[1]] + #1[[2]] == #1[[2]]^#1[[1]] & ];
Cases[possibles, {_?Positive, x_ /; x >= 0}];
ToExpression /@ StringJoin /@ Map[ToString, %, {-1}]

Out[5]=
{25}

Regards,
Jean-Marc

1. http://en.wikipedia.org/wiki/Friedman_number


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