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MathGroup Archive 2006

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Re: Number-Theory :: All-Digit Perfect Squares

  • To: mathgroup at smc.vnet.net
  • Subject: [mg64271] Re: [mg64264] Number-Theory :: All-Digit Perfect Squares
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Thu, 9 Feb 2006 02:44:37 -0500 (EST)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

test[x_]:=And@@(MemberQ[IntegerDigits[x],#]&/@Range[9]);

Select[Range[11111,31427]^2,test[#]&]


Bob Hanlon

> 
> From: bd satish <bdsatish at gmail.com>
To: mathgroup at smc.vnet.net
> Subject: [mg64271] [mg64264] Number-Theory :: All-Digit Perfect Squares
> 
>         Hi buddies,
> 
> 
>                          I set out to write a code that generates nine-digit
> perfect square numbers , with each of the digits 1,2,3,...9 occuring only 
once
> in a given number. An example is 139854276  = 11826^2 . Obviuously , 
all
> such numbers must lie in the interval [123456789 , 987654321] . Since
> 11111^2 < 123456789 and 31427^2 > 987654321 ,  all the square 
numbers must
> have their square-roots
> in the interval (11111,31427) .
> 
>               I need suggetions from you guys to help me improve the code or
> to make it better or
>  shorter.
> 
>                            The logic I used is this:
> 
>  (a).  Generate all the squares of integers in the range [11111,31427]
> 
>  (b).  Seperate the numbers into digits (using the command IntegerDigits[ ]
> )
> 
>  (c).  Check , how many (or which and all)  numbers in this list  have each
> of the digits 1,2,3,...8,9 exactly once.
> 
>  (d).  Collect all those lists and put them back as numbers (using the
> command FromDigits[ ] )
> 
> 
>            Here is the actual code:
> 
>  squares = IntegerDigits[Table[i ^ 2 , { i,11111,31427}]];
>  sel = { } ; (* empty-list*)
>  Do[
>        p = squares[[k]];
>        logic =
> And[MemberQ[p,1],MemberQ[p,2],MemberQ[p,3],MemberQ[p,4],MemberQ
[p,5],MemberQ[p,6],
>                    MemberQ[p,7],MemberQ[p,8],MemberQ[p,9] ] ;
> 
>        If[TrueQ[logic] , sel = Append[sel,p]] ,
>        {k,1,Length[squares]}
>     ];
>  Map[FromDigits,sel,{1}]
> 
>  The code does work perfectly, giving a list of 30 such  numbers.
> 
>  Will anyone help to to improve the code , if possible ?
> 
>  I would like to get rid of MemberQ[..] repeated so often.
> 
> 
> 


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