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 A102943 Numbers n such that 10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 1, 2, 8, 10, 25, 50, 76, 104, 4406, 8935, 26000, 31652 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (16*10^n+11)/9 is prime. a(13) > 10^5. - Robert Price, Feb 07 2015 LINKS Makoto Kamada, Prime numbers of the form 177...779. FORMULA a(n) = A102028(n) - 1. MATHEMATICA Do[ If[ PrimeQ[(16*10^n + 11)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A102028. Sequence in context: A209449 A002510 A247592 * A327988 A062880 A066707 Adjacent sequences:  A102940 A102941 A102942 * A102944 A102945 A102946 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 16 2004 EXTENSIONS Addition of a(11) from Kamada data by Robert Price, Dec 13 2010 a(12) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 STATUS approved

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Last modified April 7 01:11 EDT 2020. Contains 333291 sequences. (Running on oeis4.)