Truncatable primes: Difference between revisions

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print( "max_prime_right = ", max_prime_right )</lang>

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=={{header|Mathematica}}==

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<lang Mathematica>LeftTruncatablePrimeQ[n_] := Times @@ IntegerDigits[n] > 0 &&

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And @@ PrimeQ /@ ToExpression /@ StringJoin /@

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Rest[Most[NestList[Rest, #, Length[#]] &[Characters[ToString[n]]]]]

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RightTruncatablePrimeQ[n_] := Times @@ IntegerDigits[n] > 0 &&

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And @@ PrimeQ /@ ToExpression /@ StringJoin /@

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Rest[Most[NestList[Most, #, Length[#]] &[Characters[ToString[n]]]]]</lang>

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Example usage:

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<pre>n = PrimePi[1000000]; While[Not[LeftTruncatablePrimeQ[Prime[n]]], n--]; Prime[n]

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-> 998443

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n = PrimePi[1000000]; While[Not[RightTruncatablePrimeQ[Prime[n]]], n--]; Prime[n]

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-> 739399</pre>

=={{header|Maple}}==

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998443

</pre>

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=={{header|Mathematica}}==

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<lang Mathematica>LeftTruncatablePrimeQ[n_] := Times @@ IntegerDigits[n] > 0 &&

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And @@ PrimeQ /@ ToExpression /@ StringJoin /@

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Rest[Most[NestList[Rest, #, Length[#]] &[Characters[ToString[n]]]]]

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RightTruncatablePrimeQ[n_] := Times @@ IntegerDigits[n] > 0 &&

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And @@ PrimeQ /@ ToExpression /@ StringJoin /@

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Rest[Most[NestList[Most, #, Length[#]] &[Characters[ToString[n]]]]]</lang>

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Example usage:

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<pre>n = PrimePi[1000000]; While[Not[LeftTruncatablePrimeQ[Prime[n]]], n--]; Prime[n]

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-> 998443

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n = PrimePi[1000000]; While[Not[RightTruncatablePrimeQ[Prime[n]]], n--]; Prime[n]

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-> 739399</pre>

=={{header|MATLAB}}==