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Numbers k such that k3333333 is prime.
1

%I #13 Sep 08 2022 08:45:16

%S 8,10,11,22,37,59,64,71,77,82,85,89,94,98,103,109,116,119,130,134,142,

%T 145,151,154,158,166,173,178,184,215,229,236,247,250,253,259,275,298,

%U 299,301,310,316,317,323,346,347,364,380,385,389,401,406,422,425,449,460,464,467,470

%N Numbers k such that k3333333 is prime.

%H Harvey P. Dale, <a href="/A102758/b102758.txt">Table of n, a(n) for n = 1..1000</a>

%e If k=8, then k3333333 = 83333333 (prime).

%e If k=71, then k3333333 = 713333333 (prime).

%e If k=103, then k3333333 = 1033333333 (prime).

%t Select[Range[500],PrimeQ[# 10^7+3333333]&] (* _Harvey P. Dale_, Aug 28 2019 *)

%o (Magma) [ n: n in [1..700] | IsPrime(Seqint([3,3,3,3,3,3,3] cat Intseq(n))) ]; // _Vincenzo Librandi_, Feb 03 2011

%K base,nonn

%O 1,1

%A _Parthasarathy Nambi_, Feb 25 2005