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 A102962 Numbers n such that 2*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 3, 6, 18, 69, 443, 449, 455, 2459, 4745, 7973, 14249, 31710 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (26*10^n-17)/9 is prime. a(13) > 10^5. - Robert Price, Mar 28 2015 LINKS Makoto Kamada, Prime numbers of the form 288...887. FORMULA a(n) = A101971(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(26*10^n - 17)/9], Print[n]], {n, 0, 10000}] Select[Range[10000], PrimeQ[(26 10^# - 17) / 9] &] (* Vincenzo Librandi, Mar 29 2015 *) PROG (MAGMA) [n: n in [0..100] | IsPrime((26*10^n-17) div 9)]; // Vincenzo Librandi, Mar 29 2015 CROSSREFS Cf. A002275, A101971. Sequence in context: A215635 A215634 A178789 * A076510 A220816 A038060 Adjacent sequences:  A102959 A102960 A102961 * A102963 A102964 A102965 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 17 2004 EXTENSIONS Addition of a(11) from Kamada data by Robert Price, Dec 13 2010 a(12) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 STATUS approved

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Last modified September 20 04:23 EDT 2020. Contains 337264 sequences. (Running on oeis4.)