A103006 Numbers n such that 5*10^n + R_n + 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 23, 53, 12809, 15071

Offset

1,2

Comments

Also numbers n such that (46*10^n+53)/9 is prime.

a(6) > 10^5. - Robert Price, Jun 20 2015

Links

Table of n, a(n) for n=1..5.

Makoto Kamada, Prime numbers of the form 511...117.

Index entries for primes involving repunits.

Formula

a(n) = A101571(n-1) + 1.

Mathematica

Do[ If[ PrimeQ[(46*10^n + 53)/9], Print[n]], {n, 0, 10000}]
Select[Range[0, 15100], PrimeQ[FromDigits[Join[PadRight[{5}, #, 1], {7}]]]&] (* Harvey P. Dale, Mar 13 2012 *)

Crossrefs

Cf. A002275, A101571.

Sequence in context: A238854 A045345 A133986 * A053236 A118603 A303891

Adjacent sequences: A103003 A103004 A103005 * A103007 A103008 A103009

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

One more PRP term from Serge Batalov, Oct 13 2008

Addition of a(5) from Kamada data by Robert Price, Dec 13 2010

Status

approved