A103089 Numbers k such that 8*10^k + 7*R_k - 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

0, 5, 6, 185, 401, 480, 1319, 5646, 6029, 16824, 62387, 70638

Offset

1,2

Comments

Also numbers k such that (79*10^k-61)/9 is prime.

a(13) > 10^5. - Robert Price, Oct 25 2015

Links

Table of n, a(n) for n=1..12.

Makoto Kamada, Prime numbers of the form 877...771.

Index entries for primes involving repunits.

Formula

a(n) = A101076(n+1) + 1, for n>1.

Mathematica

Do[ If[ PrimeQ[(79*10^n - 61)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101076.

Sequence in context: A041257 A337465 A041411 * A041601 A301648 A041827

Adjacent sequences: A103086 A103087 A103088 * A103090 A103091 A103092

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

1 more term. Next term exceeds 50000. Sean A. Irvine, Sep 10 2009

Inserted a(1)=0 and added a(11)-a(12) by Robert Price, Oct 25 2015

Status

approved