A102937 Numbers k such that 10^k + 5*R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

0, 1, 2, 5, 7, 19, 20, 28, 58, 250, 397, 7591, 32716, 70978, 83587

Offset

1,3

Comments

Also numbers k such that (14*10^k + 13)/9 is prime.

a(16) > 10^5. - Robert Price, Jan 17 2015

Links

Table of n, a(n) for n=1..15.

Makoto Kamada, Prime numbers of the form 155...557.

Index entries for primes involving repunits.

Formula

a(n) = A102020(n-1) + 1.

Mathematica

Do[ If[ PrimeQ[(14*10^n + 13)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A102020.

Sequence in context: A173929 A173299 A097052 * A045358 A128005 A045359

Adjacent sequences: A102934 A102935 A102936 * A102938 A102939 A102940

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 16 2004

Extensions

0 added by Arkadiusz Wesolowski, Mar 10 2011

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

a(14)-a(15) from Robert Price, Jan 17 2015

Status

approved