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 A294909 Numbers k such that (10^k + 47)/3 is prime. 0
 1, 3, 5, 6, 9, 13, 120, 220, 568, 640, 666, 1205, 1600, 2479, 2482, 2939, 3077, 8649, 9520, 12407, 33421, 36162, 41190, 65340 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k > 1, numbers such that k-2 occurrences of the digit 3 followed by the digits 49 is prime (see Example section). - Robert Price, Nov 10 2017 a(25) > 2*10^5. - Robert Price, Nov 10 2017 LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 3w49 EXAMPLE 3 is in this sequence because (10^3 + 47)/3 = 349 is prime. Initial terms and associated primes: a(1) = 1, 19; a(2) = 3, 349; a(3) = 5, 33349; a(4) = 6, 333349; a(5) = 9, 333333349; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(10^# + 47)/3] &] PROG (MAGMA) [n: n in [0..500] |IsPrime((10^n+47) div 3)]; (PARI) is(n) = ispseudoprime((10^n + 47) / 3); \\ Altug Alkan, Sep 26 2016 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. See also similar sequences listed in A274986. Sequence in context: A096394 A075472 A072522 * A070111 A070117 A176345 Adjacent sequences:  A294906 A294907 A294908 * A294910 A294911 A294912 KEYWORD nonn,more,hard AUTHOR Vincenzo Librandi, Sep 26 2016 EXTENSIONS a(18)-a(24) from Robert Price, Nov 10 2017 STATUS approved

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Last modified September 25 00:01 EDT 2020. Contains 337332 sequences. (Running on oeis4.)