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 A102930 Numbers k such that 10^k + 2*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 2
 1, 2, 4, 14, 25, 32, 56, 62, 811, 812, 1084, 2533, 11924, 49552 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers k such that (11*10^k + 43)/9 is prime. a(15) > 10^5. - Robert Price, Jan 16 2015 a(15) > 2*10^5. - Tyler Busby, Feb 01 2023 LINKS Table of n, a(n) for n=1..14. Makoto Kamada, Prime numbers of the form 122...227. Index entries for primes involving repunits. FORMULA a(n) = A102010(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(11*10^n + 43)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A102010. Sequence in context: A350050 A096012 A261562 * A357996 A135113 A050564 Adjacent sequences: A102927 A102928 A102929 * A102931 A102932 A102933 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 16 2004 EXTENSIONS Addition of a(13) from Kamada data by Robert Price, Dec 12 2010 a(14) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 STATUS approved

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Last modified December 5 14:39 EST 2023. Contains 367592 sequences. (Running on oeis4.)