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 A103107 Numbers n such that 9*10^n + 8*R_n - 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 0, 6, 9, 90, 111, 210, 237, 414, 1192, 1260, 5836, 6772, 24861, 52431 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (89*10^n-71)/9 is prime. a(15) > 10^5. - Robert Price, Nov 12 2015 LINKS Table of n, a(n) for n=1..14. Makoto Kamada, Prime numbers of the form 988...881. Index entries for primes involving repunits. FORMULA a(n) = A101016(n-1) + 1, for n > 1. MATHEMATICA Do[ If[ PrimeQ[(89*10^n - 71)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101016. Sequence in context: A299917 A204383 A266006 * A121233 A156180 A191011 Adjacent sequences: A103104 A103105 A103106 * A103108 A103109 A103110 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 19 2005 EXTENSIONS a(13) from Kamada data by Robert Price, Dec 14 2010 Inserted a(1) = 0 and added a(14) from Robert Price, Nov 12 2015 STATUS approved

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Last modified April 23 20:27 EDT 2024. Contains 371916 sequences. (Running on oeis4.)