A103009 Numbers n such that 5*10^n + 2*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 4, 7, 103, 166, 280, 475, 505, 835, 922, 2018, 4435, 4459, 7615, 8558, 17164, 22801

Offset

1,2

Comments

Also numbers n such that (47*10^n+7)/9 is prime.

a(19) > 10^5. - Robert Price, Jul 10 2015

Links

Table of n, a(n) for n=1..18.

Makoto Kamada, Prime numbers of the form 522...223.

Index entries for primes involving repunits.

Formula

a(n) = A101574(n) + 1.

Mathematica

Do[ If[ PrimeQ[(46*10^n + 7)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101574.

Sequence in context: A211186 A302938 A076719 * A174393 A153662 A222011

Adjacent sequences: A103006 A103007 A103008 * A103010 A103011 A103012

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

a(17)-a(18) from Kamada data by Robert Price, Dec 14 2010

Status

approved