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Numbers k such that k333333 is prime.
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%I #23 Sep 08 2022 08:45:16

%S 10,29,31,32,34,46,50,58,62,76,79,82,83,89,100,103,109,113,115,127,

%T 137,149,151,157,158,178,184,190,194,199,205,212,218,223,236,241,257,

%U 298,302,317,326,328,337,356,358,373,386,388,395,404,409,419,449,460,464,467,479,485,488,491,502,512

%N Numbers k such that k333333 is prime.

%e If k = 10, then k333333 = 10333333 (prime);

%e if k = 58, then k333333 = 58333333 (prime);

%e if k = 100, then k333333 = 100333333 (prime).

%p q:= n-> isprime(parse(cat(n, 3$6))):

%p select(q, [$1..512])[]; # _Alois P. Heinz_, Oct 29 2021

%t Select[Range[550],PrimeQ[FromDigits[Join[IntegerDigits[#],{3,3,3,3,3,3}]]]&] (* _Harvey P. Dale_, Apr 13 2012 *)

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

%o (PARI) is(n)=isprime(n*10^6+333333) \\ _Charles R Greathouse IV_, May 15 2013

%o (Python)

%o from sympy import isprime

%o def aupto(limit):

%o return [k for k in range(limit+1) if isprime(int(str(k) + "333333"))]

%o print(aupto(512)) # _Michael S. Branicky_, Oct 29 2021

%K base,nonn

%O 1,1

%A _Parthasarathy Nambi_, Feb 24 2005