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 A102990 Numbers n such that 4*10^n + 3*R_n + 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 2
 2, 3, 6, 11, 15, 26, 28, 51, 150, 182, 228, 407, 638, 3581, 4125, 4983, 5666, 15890, 27743, 43362, 55367, 60744, 73701 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (13*10^n+17)/3 is prime. a(24) > 10^5. - Robert Price, Jun 25 2015 LINKS Makoto Kamada, Prime numbers of the form 433...339. FORMULA a(n) = A101725(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(13*10^n + 17)/3], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101725. Sequence in context: A005211 A298702 A076307 * A138519 A138520 A210458 Adjacent sequences:  A102987 A102988 A102989 * A102991 A102992 A102993 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 17 2005 EXTENSIONS Addition of a(18)-a(19) from Kamada data by Robert Price, Dec 10 2010 a(20) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013 a(21)-a(23) from Robert Price, Jun 25 2015 STATUS approved

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Last modified April 6 11:38 EDT 2020. Contains 333273 sequences. (Running on oeis4.)