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 A279549 Numbers k such that (13*10^k + 47) / 3 is prime. 0
 1, 2, 3, 9, 10, 14, 36, 44, 69, 124, 249, 297, 453, 535, 766, 1074, 1668, 1975, 1987, 2295, 5703, 6526, 13329, 34738, 37549, 39825, 93236, 99508, 136687 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 49 is prime (see Example section). a(30) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 43w49. EXAMPLE 3 is in this sequence because (13*10^3 + 47) / 3 = 4349 is prime. Initial terms and primes associated: a(1) = 1, 59; a(2) = 2, 449; a(3) = 3, 4349; a(4) = 9, 4333333349; a(5) = 10, 43333333349; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(13*10^# + 47) / 3] &] PROG (PARI) is(n)=ispseudoprime((13*10^n + 47)/3) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A057291 A135107 A191568 * A030743 A098020 A047358 Adjacent sequences:  A279546 A279547 A279548 * A279550 A279551 A279552 KEYWORD nonn,more,hard AUTHOR Robert Price, Jan 05 2017 EXTENSIONS a(29) from Robert Price, Oct 14 2018 STATUS approved

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Last modified September 21 08:38 EDT 2020. Contains 337268 sequences. (Running on oeis4.)