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%I #17 Sep 08 2022 08:45:19
%S 3,17,23,27,41,53,57,59,89,93,101,137,141,153,167,171,191,201,213,237,
%T 239,243,249,261,263,267,269,279,291,317,323,339,347,351,359,369,377,
%U 383,417,419,431,447,471,477,479,489,491,509,513,521,527,543,549,551
%N Numbers n such that the string 77n is prime.
%H Vincenzo Librandi, <a href="/A109990/b109990.txt">Table of n, a(n) for n = 1..2000</a>
%e If n=3 then 77n = 773 (prime).
%e If n=93 then 77n = 7793 (prime).
%p select(n -> isprime(77*10^(1+ilog10(n))+n), [$1..1000]); # _Robert Israel_, Jul 30 2014
%t Select[Range[700], PrimeQ[77 10^IntegerLength[#] + #] &] (* _Vincenzo Librandi_, Jul 30 2014 *)
%o (Magma) [n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [7, 7])) ]; // _Vincenzo Librandi_, Jul 30 2014
%K nonn,base
%O 1,1
%A _Parthasarathy Nambi_, Sep 01 2005
%E More terms from _Vincenzo Librandi_, Mar 27 2010
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