A103021 Numbers n such that 5*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 3, 7, 15, 27, 129, 189, 333, 1324, 1600, 2199, 10000, 27751

Offset

1,3

Comments

Also numbers n such that (52*10^n+11)/9 is prime.

a(15) > 10^5. - Robert Price, Sep 05 2015

Links

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 577...779.

Index entries for primes involving repunits.

Formula

a(n) = A101586(n-1) + 1, for n>1.

Example

For n=0, (52*10^n+11)/9=7 which is prime, so 0 is in the sequence.

Mathematica

Do[ If[ PrimeQ[(52*10^n + 11)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101586.

Sequence in context: A343440 A147394 A350370 * A025587 A101498 A027965

Adjacent sequences: A103018 A103019 A103020 * A103022 A103023 A103024

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

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

Inserted a(1)=0 by Robert Price, Sep 05 2015

Status

approved