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Primes square (Posted on 2014-02-07) Difficulty: 3 of 5
Create a 4x4 array of digits such that:

the 4 rows read from left to right are prime numbers with digits in non-increasing order;

the 4 columns read from top to bottom are prime numbers with digits in non-increasing order;

and the 8 primes are all different.

The solution is unique.

No Solution Yet Submitted by Jer    
Rating: 3.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Computer approach (spoiler) Comment 1 of 1
Brute force mostly..

A=Select[Map[IntegerDigits,Select[Range[1000,9999],PrimeQ]],Sort[#,Greater]==#&];
S=Subsets[A,{4}];
Do[P=Permutations[s];
  Do[If[Union[Map[OddQ,p[[4]]]]=={True},
    T=Transpose[p];
    If[Intersection[T,p]=={},
     If[Union[Map[MemberQ[A,#]&,T]]=={True},Print[MatrixForm[p]]]]],
   {p,P}],
  {s,S}];

which gives:

9 8 8 7
9 6 4 3
7 6 4 3
3 3 3 1

and its transpose.




  Posted by Harry on 2014-02-09 16:21:00
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