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 A256760 Numbers k such that R_k + 60 is prime, where R_k = 11...1 is the repunit (A002275) of length n. 0
 1, 2, 4, 5, 8, 17, 19, 64, 368, 616, 857, 4351, 6526, 10555, 12685, 14549, 33886 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also, numbers k such that (10^k + 539)/9 is prime. Terms from Kamada data.  Note Kamada does not recognize k=1 as 61 is a degenerate case of form AAA..ABA. a(18) > 2.5*10^5. LINKS Makoto Kamada, Near-repdigit numbers of the form AA...AABA. Makoto Kamada, Prime numbers of the form 11...1171. EXAMPLE For k=5, R_5 + 60 = 11111 + 60 = 11171 which is prime. MATHEMATICA Select[Range[0, 250000], PrimeQ[(10^# + 539)/9] &] PROG (MAGMA) [n: n in [1..400] | IsPrime((10^n+539) div 9)]; // Vincenzo Librandi, Apr 10 2015 CROSSREFS Cf. A002275. Sequence in context: A045581 A253426 A092061 * A281646 A240460 A239405 Adjacent sequences:  A256757 A256758 A256759 * A256761 A256762 A256763 KEYWORD nonn,more,hard AUTHOR Robert Price, Apr 09 2015 STATUS approved

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Last modified March 28 11:00 EDT 2020. Contains 333083 sequences. (Running on oeis4.)