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 A103061 Numbers n such that 7*10^n + 5*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 0, 1, 4, 18, 19, 646, 814, 5794, 16524, 19495, 26010, 29238, 72120 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also numbers n such that (68*10^n-23)/9 is prime. a(14) > 10^5. - Robert Price, Oct 01 2015 LINKS Makoto Kamada, Prime numbers of the form 755...553. FORMULA a(n) = A101144(n-1) + 1 for n>1. MATHEMATICA Do[ If[ PrimeQ[(68*10^n - 23)/9], Print[n]], {n, 0, 10000}] Select[Range[10000], PrimeQ[(68 10^# - 23)/9] &] (* Vincenzo Librandi, Oct 02 2015 *) PROG (MAGMA) [n: n in [0..100]| IsPrime((68*10^n-23) div 9)]; // Vincenzo Librandi, Oct 02 2015 (PARI) for(n=0, 1e4, if (isprime((68*10^n-23)/9), print1(n", "))) \\ Altug Alkan, Oct 02 2015 CROSSREFS Cf. A002275, A101144. Sequence in context: A081420 A039277 A045019 * A230605 A201880 A022384 Adjacent sequences:  A103058 A103059 A103060 * A103062 A103063 A103064 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 19 2005 EXTENSIONS a(9)-a(12) from Kamada data by Robert Price, Dec 14 2010 a(1)=0 inserted and a(13) added by Robert Price, Oct 01 2015 STATUS approved

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Last modified May 25 15:44 EDT 2019. Contains 323572 sequences. (Running on oeis4.)