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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 22 02:58 EST 2019. Contains 329383 sequences. (Running on oeis4.)