

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
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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

Table of n, a(n) for n=1..31.
Makoto Kamada, Prime numbers of the form 166...667.
Index entries for primes involving repunits


FORMULA

a(n) = A102024(n1) + 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



