A103008 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.

2, 9, 12, 15, 26, 45, 62, 80, 128, 326, 494, 614, 710, 1641, 1646, 2103, 8514, 8688

Offset

1,1

Comments

Also numbers n such that (47*10^n-11)/9 is prime.

No other terms below 50000.

a(19) > 10^5. - Robert Price, Jul 04 2015

Links

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

Makoto Kamada, Prime numbers of the form 522...221.

Index entries for primes involving repunits.

Formula

a(n) = A101573(n) + 1.

Mathematica

Do[ If[ PrimeQ[(47*10^n - 11)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101573.

Sequence in context: A207967 A265413 A297830 * A124742 A152003 A251428

Adjacent sequences: A103005 A103006 A103007 * A103009 A103010 A103011

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Status

approved