A103053 Numbers n such that 7*10^n + 2*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 4, 12, 13, 15, 36, 40, 90, 837, 2424, 2427, 2443, 15925, 16212

Offset

1,2

Comments

Also numbers n such that (65*10^n+7)/9 is prime.

a(15) > 10^5. - Robert Price, Sep 22 2015

Links

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

Makoto Kamada, Prime numbers of the form 722...223.

Index entries for primes involving repunits.

Formula

a(n) = A101134(n) + 1.

Mathematica

Do[ If[ PrimeQ[(65*10^n + 7)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101134.

Sequence in context: A051434 A074138 A120252 * A087760 A237279 A032498

Adjacent sequences: A103050 A103051 A103052 * A103054 A103055 A103056

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(13)-a(14) from Kamada data by Robert Price, Dec 14 2010

Status

approved