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 A103059 Numbers n such that 7*10^n + 4*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 1, 4, 7, 34, 82, 451, 772, 2554, 6250, 15137, 20074, 37378, 53068 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (67*10^n+41)/9 is prime. a(14) > 10^5. - Robert Price, Sep 27 2015 LINKS Makoto Kamada, Prime numbers of the form 744...449. FORMULA a(n) = A101142(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(67*10^n + 41)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101142. Sequence in context: A237424 A143547 A149090 * A123809 A140981 A283819 Adjacent sequences:  A103056 A103057 A103058 * A103060 A103061 A103062 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 19 2005 EXTENSIONS a(10)-a(11) from Kamada data by Robert Price, Dec 14 2010 a(12) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 a(13) from Robert Price, Sep 27 2015 STATUS approved

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Last modified May 11 00:21 EDT 2021. Contains 343784 sequences. (Running on oeis4.)