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 A103097 Numbers n such that 9*10^n + 4*R_n - 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 2, 4, 8, 2960, 4571, 5201, 17864, 21922, 89375 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (85*10^n-31)/9 is prime. a(10) > 10^5. - Robert Price, Nov 07 2015 LINKS Makoto Kamada, Prime numbers of the form 944...441. FORMULA a(n) = A101006(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(85*10^n - 31)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101006. Sequence in context: A012456 A071686 A296742 * A062286 A071071 A195729 Adjacent sequences:  A103094 A103095 A103096 * A103098 A103099 A103100 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 19 2005 EXTENSIONS a(7)-a(8) from Kamada data by Robert Price, Dec 14 2010 a(9) from Robert Price, Nov 07 2015 STATUS approved

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Last modified October 18 22:57 EDT 2019. Contains 328211 sequences. (Running on oeis4.)