A103014 Numbers n such that 5*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 3, 4, 9, 12, 60, 268, 289, 384, 795, 3474, 9180, 76438

Offset

1,2

Comments

Also numbers n such that (49*10^n-13)/9 is prime.

a(14) > 10^5. - Robert Price, Jul 16 2015

Links

Table of n, a(n) for n=1..13.

Makoto Kamada, Prime numbers of the form 544...443.

Index entries for primes involving repunits.

Formula

a(n) = A101579(n) + 1.

Mathematica

Do[ If[ PrimeQ[(49*10^n - 13)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101579.

Sequence in context: A211221 A029448 A249179 * A116552 A339996 A225288

Adjacent sequences: A103011 A103012 A103013 * A103015 A103016 A103017

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

a(13) from Robert Price, Jul 16 2015

Status

approved