A107642 Numbers k such that the string 57k is prime.

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

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