A102929 Numbers k such that 10^k + 2*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

0, 1, 3, 9, 48, 58, 153, 261, 876, 1179, 1596, 17715, 63718

Offset

1,3

Comments

Also numbers k such that (11*10^k + 7)/9 is prime.

a(14) > 10^5. - Robert Price, Nov 15 2014

a(14) > 2*10^5. - Tyler Busby, Feb 01 2023

Links

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

Makoto Kamada, Prime numbers of the form 122...223.

Index entries for primes involving repunits

Formula

a(n) = A102009(n-1) + 1.

Mathematica

Do[ If[ PrimeQ[(11*10^n + 7)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A102009.

Sequence in context: A129432 A111551 A258481 * A105458 A366485 A306947

Adjacent sequences: A102926 A102927 A102928 * A102930 A102931 A102932

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 16 2004

Extensions

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

Inserted a(1)=0 by Robert Price, Nov 15 2014

a(13) from Kamada data by Robert Price, Nov 15 2014

Status

approved