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 A102972 Numbers n such that 3*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 0, 1, 3, 6, 12, 33, 69, 111, 1965, 5646, 7404, 11103, 20790, 24840, 38199, 90669 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also numbers n such that (32*10^n+13)/9 is prime. a(17) > 10^5. - Robert Price, Apr 07 2015 LINKS Makoto Kamada, Prime numbers of the form 355...557. FORMULA a(n) = A101837(n-1) + 1. MATHEMATICA Do[ If[ PrimeQ[(32*10^n+13)/9], Print[n]], {n, 0, 10000}] Select[Range[0, 10000], PrimeQ[(32 10^# + 13) / 9 ] &] (* Vincenzo Librandi, Apr 08 2015 *) PROG (MAGMA) [n: n in [0..200] | IsPrime((32*10^n+13) div 9)]; // Vincenzo Librandi, Apr 08 2015 CROSSREFS Cf. A002275, A101837. Sequence in context: A026079 A066710 A033648 * A075209 A075207 A208131 Adjacent sequences:  A102969 A102970 A102971 * A102973 A102974 A102975 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 17 2004 EXTENSIONS Addition of a(12)-a(14) from Kamada data by Robert Price, Dec 13 2010 a(15) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 a(16) from Robert Price, Apr 07 2015 STATUS approved

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Last modified October 16 05:41 EDT 2019. Contains 328044 sequences. (Running on oeis4.)