A103020 Numbers n such that 5*10^n + 7*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 4, 12, 15, 18, 37, 109, 1728, 2482, 3480, 6577, 9015, 16162, 45349

Offset

1,2

Comments

Also numbers n such that (52*10^n-43)/9 is prime.

a(15) > 10^5. - Robert Price, Sep 09 2015

Links

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

Makoto Kamada, Prime numbers of the form 577...773.

Index entries for primes involving repunits.

Formula

a(n) = A101585(n) + 1.

Mathematica

Do[ If[ PrimeQ[(52*10^n - 43)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101585.

Sequence in context: A260257 A256706 A340869 * A215011 A024353 A024354

Adjacent sequences: A103017 A103018 A103019 * A103021 A103022 A103023

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

a(14) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Status

approved