

A102975


Numbers n such that 3*10^n + 6*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


2



1, 2, 12, 15, 51, 194, 498, 2136, 2822, 3762, 7428, 22740, 30452, 37952, 55254
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OFFSET

1,2


COMMENTS

Also numbers n such that (11*10^n+1)/3 is prime.
a(16) > 10^5.  Robert Price, Jan 29 2015


LINKS

Table of n, a(n) for n=1..15.
Makoto Kamada, Prime numbers of the form 366...667.
Index entries for primes involving repunits.


FORMULA

a(n) = A101840(n) + 1.


MATHEMATICA

Do[ If[ PrimeQ[(11*10^n+1)/3], Print[n]], {n, 0, 10000}]


PROG

(MAGMA) [n: n in [0..300]  IsPrime((11*10^n+1) div 3)]; // Vincenzo Librandi, Dec 01 2015


CROSSREFS

Cf. A002275, A101840.
Sequence in context: A077103 A036499 A107607 * A120300 A089021 A176888
Adjacent sequences: A102972 A102973 A102974 * A102976 A102977 A102978


KEYWORD

more,nonn


AUTHOR

Robert G. Wilson v, Dec 17 2004


EXTENSIONS

Addition of a(12) from Kamada data by Robert Price, Dec 13 2010
a(13)a(14) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
a(15) from Kamada data by Robert Price, Jan 29 2015


STATUS

approved



