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 A109990 Numbers n such that the string 77n is prime. 1
 3, 17, 23, 27, 41, 53, 57, 59, 89, 93, 101, 137, 141, 153, 167, 171, 191, 201, 213, 237, 239, 243, 249, 261, 263, 267, 269, 279, 291, 317, 323, 339, 347, 351, 359, 369, 377, 383, 417, 419, 431, 447, 471, 477, 479, 489, 491, 509, 513, 521, 527, 543, 549, 551 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..2000 EXAMPLE If n=3 then 77n = 773 (prime). If n=93 then 77n = 7793 (prime). MAPLE select(n -> isprime(77*10^(1+ilog10(n))+n), [\$1..1000]); # Robert Israel, Jul 30 2014 MATHEMATICA Select[Range[700], PrimeQ[77 10^IntegerLength[#] + #] &] (* Vincenzo Librandi, Jul 30 2014 *) PROG (MAGMA) [n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [7, 7])) ]; // Vincenzo Librandi, Jul 30 2014 CROSSREFS Sequence in context: A298469 A173579 A093024 * A019369 A019380 A296937 Adjacent sequences:  A109987 A109988 A109989 * A109991 A109992 A109993 KEYWORD nonn,base AUTHOR Parthasarathy Nambi, Sep 01 2005 EXTENSIONS More terms from Vincenzo Librandi, Mar 27 2010 STATUS approved

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Last modified August 4 20:11 EDT 2021. Contains 346455 sequences. (Running on oeis4.)