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 A109355 Numbers k such that the string 23572357k is prime. 1
 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 (list; graph; refs; listen; history; text; internal format)
 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: A117609 A122072 A261338 * A272404 A274971 A040045 Adjacent sequences:  A109352 A109353 A109354 * A109356 A109357 A109358 KEYWORD nonn,base AUTHOR Parthasarathy Nambi, Aug 22 2005 STATUS approved

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Last modified July 23 22:20 EDT 2021. Contains 346265 sequences. (Running on oeis4.)