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 A102941 Numbers k such that 10^k + 6*R_k + 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 1
 1, 3, 5, 7, 11, 12, 28, 36, 384, 629, 720, 1398, 2002, 2622, 6457, 19305, 38508, 46455, 95976 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers k such that (5*10^k + 7)/3 is prime. a(20) > 10^5. - Robert Price, Nov 15 2014 LINKS Makoto Kamada, Prime numbers of the form 166...669. FORMULA a(n) = A102025(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(5*10^n + 7)/3], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A102025. Sequence in context: A152212 A249370 A282810 * A114235 A285848 A086527 Adjacent sequences:  A102938 A102939 A102940 * A102942 A102943 A102944 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 16 2004 EXTENSIONS Addition of a(16) from Kamada data by Robert Price, Dec 12 2010 a(17)-a(18) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 a(19) from Kamada data by Robert Price, Nov 15 2014 STATUS approved

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Last modified December 7 00:16 EST 2019. Contains 329812 sequences. (Running on oeis4.)