A109355 Numbers k such that the string 23572357k is prime.

7, 19, 31, 37, 43, 57, 61, 103, 169, 213, 229, 243, 273, 337, 339, 349, 357, 387, 421, 441, 453, 463, 469, 483, 531, 541, 559, 577, 583, 597, 621, 631, 637, 643, 681, 687, 729, 759, 789, 819, 877, 901, 927, 931, 937, 1011, 1033, 1047, 1051, 1071, 1077, 1093, 1101, 1141, 1143, 1201

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

k=7 is in the sequence because 23572357k = 235723577 is prime.
k=213 is in the sequence because 23572357k = 23572357213 is prime.

Maple

q:= 23572357:
select(n -> isprime(q*10^(1+ilog10(n))+n), [seq(i, i=1..10000, 2)]); # Robert Israel, Jan 22 2018

Mathematica

Select[Range[1250], PrimeQ[23572357*10^IntegerLength[#] + #] &] (* Michael De Vlieger, Jan 22 2018 *)

Prog

(Magma) [ n: n in [1..1750] | IsPrime(Seqint(Intseq(n) cat [7, 5, 3, 2, 7, 5, 3, 2])) ]; // Vincenzo Librandi, Feb 02 2011

Crossrefs

Sequence in context: A122072 A261338 A352338 * A272404 A274971 A040045

Adjacent sequences: A109352 A109353 A109354 * A109356 A109357 A109358

Keyword

nonn,base

Author

Parthasarathy Nambi, Aug 22 2005

Status

approved