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 A103098 Numbers n such that 9*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 30, 41, 228, 581, 1290, 2580, 3696, 11390, 21558 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (85*10^n-13)/9 is prime. a(10) > 10^5. - Robert Price, Nov 05 2015 LINKS Makoto Kamada, Prime numbers of the form 944...443. FORMULA a(n) = A101007(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(85*10^n - 13)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101007. Sequence in context: A043120 A039297 A043900 * A110849 A074696 A127663 Adjacent sequences: A103095 A103096 A103097 * A103099 A103100 A103101 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 19 2005 EXTENSIONS a(8)-a(9) from Kamada data by Robert Price, Dec 14 2010 STATUS approved

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Last modified December 1 18:55 EST 2022. Contains 358475 sequences. (Running on oeis4.)