

A107642


Numbers k such that the string 57k is prime.


2



1, 7, 11, 17, 37, 41, 43, 49, 79, 83, 91, 107, 119, 131, 139, 143, 149, 163, 173, 179, 191, 193, 203, 221, 223, 241, 251, 259, 269, 271, 283, 287, 301, 329, 331, 347, 349, 367, 373, 383, 389, 397, 413, 427, 457, 467, 487, 493, 503, 527, 529, 557, 559, 571, 587
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OFFSET

1,2


LINKS



EXAMPLE

k=1 is in the sequence because 57k = 571 is prime.
k=41 is in the sequence because 57k = 5741 is prime.
k=83 is in the sequence because 57k = 5783 is prime.


MATHEMATICA

Select[Range[600], PrimeQ[57*10^IntegerLength[#] + #] &] (* Michael De Vlieger, Jan 22 2018 *)


PROG

(PARI) for(n=1, 1000, if(isprime(eval(concat("57", n))), print1(n, ", "))) \\ Rick L. Shepherd, Jun 13 2005
(Magma) [ n: n in [1..700]  IsPrime(Seqint(Intseq(n) cat [7, 5])) ]; // Vincenzo Librandi, Feb 02 2011


CROSSREFS



KEYWORD

nonn,base


AUTHOR



EXTENSIONS



STATUS

approved



