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Numbers k such that k33333 is prime.
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%I #17 Sep 08 2022 08:45:16

%S 7,11,26,28,32,34,37,44,49,56,62,64,70,85,95,103,106,110,119,121,125,

%T 127,130,134,140,142,154,166,167,170,176,181,209,215,217,236,259,275,

%U 277,281,293,296,307,313,319,320,323,329,337,343,347,349,370,376,379,382,392,400,407,412,415,424,431

%N Numbers k such that k33333 is prime.

%e If k=7, then k33333 = 733333 (prime).

%e If k=49, then k33333 = 4933333 (prime).

%e If k=95, then k33333 = 9533333 (prime).

%t Select[Range[500],PrimeQ[FromDigits[Join[IntegerDigits[#],{3,3,3,3,3} ]]]&] (* _Harvey P. Dale_, Jun 20 2011 *)

%o (Magma) [ n: n in [1..700] | IsPrime(Seqint([3,3,3,3,3] cat Intseq(n))) ]; // _Vincenzo Librandi_, Feb 04 2011

%K base,nonn

%O 1,1

%A _Parthasarathy Nambi_, Feb 22 2005