A102963 Numbers n such that 2*10^n + 8*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 7, 8, 11, 14, 19, 32, 41, 53, 61, 133, 157, 239, 1237, 30254, 34423, 139289

Offset

1,3

Comments

Also numbers n such that (26*10^n+1)/9 is prime.

Links

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

Makoto Kamada, Prime numbers of the form 288...889.

Index entries for primes involving repunits.

Formula

a(n) = A101972(n-1) + 1.

Mathematica

Do[ If[ PrimeQ[(26*10^n + 1)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101972.

Sequence in context: A090385 A350694 A145826 * A117619 A226977 A098731

Adjacent sequences: A102960 A102961 A102962 * A102964 A102965 A102966

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

a(16)-a(18) from Kamada data by Robert Price, Dec 14 2010

Status

approved