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 A102940 Numbers n such that 10^n + 6*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 3
 0, 1, 2, 3, 5, 9, 11, 14, 32, 54, 55, 60, 153, 200, 461, 569, 840, 847, 1296, 1356, 2007, 2627, 2847, 3110, 6876, 9161, 17765, 33555, 59142, 65773, 280710 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also numbers n such that (5*10^n+1)/3 is prime. Numbers n such that A126109(n) is prime. a(32) > 3*10^5. - Robert Price, Nov 15 2014 LINKS Makoto Kamada, Prime numbers of the form 166...667. FORMULA a(n) = A102024(n-1) + 1. MAPLE A102940:=n->`if`(isprime((5*10^n+1)/3), n, NULL): seq(A102940(n), n=0..1000); # Wesley Ivan Hurt, Nov 15 2014 MATHEMATICA Do[ If[ PrimeQ[(5*10^n + 1)/3], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A000040, A002275, A102024, A126109. Sequence in context: A137518 A137509 A014109 * A157049 A195668 A324698 Adjacent sequences:  A102937 A102938 A102939 * A102941 A102942 A102943 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 16 2004 EXTENSIONS Edited by N. J. A. Sloane, Mar 16 2007 Addition of a(27) from Kamada data by Robert Price, Dec 08 2010 a(28) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 a(29)-a(31) from Kamada data by Robert Price, Nov 15 2014 STATUS approved

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Last modified June 24 21:16 EDT 2019. Contains 324337 sequences. (Running on oeis4.)