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 A103020 Numbers n such that 5*10^n + 7*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 1, 4, 12, 15, 18, 37, 109, 1728, 2482, 3480, 6577, 9015, 16162, 45349 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (52*10^n-43)/9 is prime. a(15) > 10^5. - Robert Price, Sep 09 2015 LINKS Makoto Kamada, Prime numbers of the form 577...773. FORMULA a(n) = A101585(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(52*10^n - 43)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101585. Sequence in context: A310563 A260257 A256706 * A215011 A024353 A024354 Adjacent sequences:  A103017 A103018 A103019 * A103021 A103022 A103023 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 18 2005 EXTENSIONS Addition of a(13) from Kamada data by Robert Price, Dec 13 2010 a(14) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 STATUS approved

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Last modified November 17 00:14 EST 2018. Contains 317275 sequences. (Running on oeis4.)