A102977 Numbers k such that 3*10^k + 7*R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

0, 2, 3, 5, 6, 20, 776, 1185, 3164, 4212, 10733, 21726, 38235

Offset

1,2

Comments

Also numbers k such that (34*10^k+11)/9 is prime.

a(14) > 10^5. - Robert Price, May 08 2015

Links

Table of n, a(n) for n=1..13.

Makoto Kamada, Prime numbers of the form 377...779.

Index entries for primes involving repunits.

Formula

a(n) = A101843(n-1) + 1.

Mathematica

Do[ If[ PrimeQ[(34*10^n + 11)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101843.

Sequence in context: A109628 A192367 A227230 * A238335 A131599 A263650

Adjacent sequences: A102974 A102975 A102976 * A102978 A102979 A102980

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

Addition of a(11)-a(12) from Kamada data by Robert Price, Dec 13 2010

a(13) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Status

approved