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 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Michael De Vlieger, Table of n, a(n) for n = 1..10000 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 Sequence in context: A156112 A158594 A215419 * A079651 A178386 A097956 Adjacent sequences:  A107639 A107640 A107641 * A107643 A107644 A107645 KEYWORD nonn,base AUTHOR Parthasarathy Nambi, Jun 09 2005 EXTENSIONS More terms from Rick L. Shepherd, Jun 13 2005 STATUS approved

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Last modified September 20 01:54 EDT 2020. Contains 337260 sequences. (Running on oeis4.)