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Numbers k such that k777777 is prime.
2

%I #11 Jan 24 2020 14:51:38

%S 16,20,43,50,61,62,64,83,85,100,101,103,109,113,124,131,134,136,137,

%T 139,142,145,158,160,164,172,181,197,202,205,206,251,256,262,268,272,

%U 278,289,295,298,307,310,314,316,326,347,349,359,361,362,368,373,400,419,428,431,433,437,445

%N Numbers k such that k777777 is prime.

%H Daniel Starodubtsev, <a href="/A102544/b102544.txt">Table of n, a(n) for n = 1..10000</a>

%e If k=16, then k777777 = 16777777 (prime).

%e If k=85, then k777777 = 85777777 (prime).

%e If k=124, then k777777 = 124777777 (prime).

%o [ n: n in [1..700] | IsPrime(Seqint([7,7,7,7,7,7] cat Intseq(n))) ]; // _Vincenzo Librandi_, Feb 04 2011

%K base,nonn

%O 1,1

%A _Parthasarathy Nambi_, Feb 24 2005

%E More terms from _Vincenzo Librandi_, Feb 04 2011