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 A102992 Numbers n such that 4*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 3
 1, 2, 4, 5, 13, 22, 25, 28, 38, 67, 142, 284, 295, 380, 397, 1217, 1640, 2885, 3286, 7735, 29306 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (41*10^n+13)/9 is prime. a(22) > 10^5. - Robert Price, May 22 2015 LINKS Makoto Kamada, Prime numbers of the form 455...557. FORMULA a(n) = A101727(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(41*10^n + 13)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101727. Sequence in context: A079407 A078652 A289491 * A273097 A232207 A136563 Adjacent sequences:  A102989 A102990 A102991 * A102993 A102994 A102995 KEYWORD more,nonn,changed AUTHOR Robert G. Wilson v, Jan 17 2005 EXTENSIONS Addition of a(21) from Kamada data by Robert Price, Dec 09 2010 STATUS approved

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Last modified January 20 04:14 EST 2019. Contains 319323 sequences. (Running on oeis4.)