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 A103008 Numbers n such that 5*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 2, 9, 12, 15, 26, 45, 62, 80, 128, 326, 494, 614, 710, 1641, 1646, 2103, 8514, 8688 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (47*10^n-11)/9 is prime. No other terms below 50000. a(19) > 10^5. - Robert Price, Jul 04 2015 LINKS Makoto Kamada, Prime numbers of the form 522...221. FORMULA a(n) = A101573(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(47*10^n - 11)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101573. Sequence in context: A207967 A265413 A297830 * A124742 A152003 A251428 Adjacent sequences: A103005 A103006 A103007 * A103009 A103010 A103011 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 18 2005 STATUS approved

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Last modified November 29 08:47 EST 2022. Contains 358422 sequences. (Running on oeis4.)