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.

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

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