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 A103015 Numbers n such that 5*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 2, 6, 8, 18, 53, 68, 242, 276, 320, 564, 620, 1782, 2340, 2454, 5765, 15530, 15605, 22938 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (49*10^n+23)/9 is prime. a(19) > 10^5. - Robert Price, Jul 29 2015 LINKS Makoto Kamada, Prime numbers of the form 544...447. FORMULA a(n) = A101580(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(49*10^n + 23)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101580. Sequence in context: A102656 A163911 A077638 * A098092 A221316 A106164 Adjacent sequences:  A103012 A103013 A103014 * A103016 A103017 A103018 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 18 2005 EXTENSIONS a(16)-a(18) from Kamada data by Robert Price, Dec 14 2010 STATUS approved

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