A102974 Numbers k such that 3*10^k + 6*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 6, 11, 13, 19, 23, 67, 108, 118, 176, 673, 780, 1088, 1219, 1656, 6245, 10739, 12590, 17513, 26000, 32544, 53274, 131784

Offset

1,2

Comments

Also numbers k such that (11*10^k-17)/3 is prime.

a(24) > 2*10^5. - Robert Price, Jun 10 2018

Links

Table of n, a(n) for n=1..23.

Makoto Kamada, Prime numbers of the form 366...661.

Index entries for primes involving repunits.

Formula

a(n) = A101839(n) + 1.

Mathematica

Do[ If[ PrimeQ[(11*10^k - 17)/3], Print[k]], {k, 1, 10000}]

Crossrefs

Cf. A002275, A101839.

Sequence in context: A315368 A315369 A350675 * A315370 A315371 A315372

Adjacent sequences: A102971 A102972 A102973 * A102975 A102976 A102977

Keyword

nonn,more

Author

Robert G. Wilson v, Dec 17 2004

Extensions

Addition of a(17)-a(20) from Kamada data by Robert Price, Dec 10 2010

a(21) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(22) from Kamada data by Robert Price, Jan 29 2015

a(23) from Robert Price, Jun 10 2018

0 removed by Georg Fischer, Jan 03 2021

Status

approved