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MathGroup Archive 1995

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Re: Re: SuperPrimes

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg668] Re: [mg632] Re: [mg622] SuperPrimes
  • From: Roman Maeder <maeder at inf.ethz.ch>
  • Date: Sat, 08 Apr 1995 11:37:13 +0200

villegas at wri.com (Robert Villegas) writes:

> My induction step is pretty much a brute-force search of possibilities.
> Maybe some number theory knowledge could be brought to bear on this
> for a much better overall method.
> 
> 
> Here's an implementation of this approach:
> 
> 
> superPrime[n_] :=
>   Nest[Flatten[#, 1]& @ Map[Select[10 # + {1, 3, 5, 7, 9}, PrimeQ]&, #] &,
>     {2, 3, 5, 7}, n - 1]

some number theory knowledge can indeed be applied: a prime can never end
in a 5 (unless it's the only digit), so you can delete that case from the
iteration:

superPrime[n_] :=
  Nest[Flatten[#, 1]& @ Map[Select[10 # + {1, 3, 7, 9}, PrimeQ]&, #] &,
    {2, 3, 5, 7}, n - 1]

Roman Maeder



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