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 A102970 Numbers n such that 3*10^n + 4*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 2, 3, 6, 12, 36, 39, 44, 90, 258, 512, 1482, 2378, 2406, 3224, 3378, 3876, 4161, 5510, 7425, 97242 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (31*10^n+41)/9 is prime. a(21) > 10^5. - Robert Price, Apr 04 2015 LINKS Makoto Kamada, Prime numbers of the form 344...449. FORMULA a(n) = A101834(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(31*10^n+41)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101834. Sequence in context: A213242 A243299 A096746 * A144771 A187013 A295324 Adjacent sequences:  A102967 A102968 A102969 * A102971 A102972 A102973 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 17 2004 EXTENSIONS a(20) from Robert Price, Apr 04 2015 STATUS approved

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Last modified September 23 16:09 EDT 2020. Contains 337311 sequences. (Running on oeis4.)