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 A102937 Numbers k such that 10^k + 5*R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 3
 0, 1, 2, 5, 7, 19, 20, 28, 58, 250, 397, 7591, 32716, 70978, 83587, 140693 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also numbers k such that (14*10^k + 13)/9 is prime. a(16) > 10^5. - Robert Price, Jan 17 2015 LINKS Table of n, a(n) for n=1..16. Makoto Kamada, Prime numbers of the form 155...557. Index entries for primes involving repunits. FORMULA a(n) = A102020(n-1) + 1. MATHEMATICA Do[ If[ PrimeQ[(14*10^n + 13)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A102020. Sequence in context: A173929 A173299 A097052 * A045358 A128005 A045359 Adjacent sequences: A102934 A102935 A102936 * A102938 A102939 A102940 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 16 2004 EXTENSIONS 0 added by Arkadiusz Wesolowski, Mar 10 2011 a(13) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 a(14)-a(15) from Robert Price, Jan 17 2015 a(16) from Kamada data by Tyler Busby, Apr 30 2024 STATUS approved

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Last modified May 26 14:50 EDT 2024. Contains 372826 sequences. (Running on oeis4.)