A102960 Numbers n such that 2*10^n + 8*R_n - 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

2, 12, 27, 44, 80, 119, 131, 275, 315, 876, 1307, 10895, 17105, 60717

Offset

1,1

Comments

Also numbers n such that (26*10^n-71)/9 is prime.

a(15) > 10^5. - Robert Price, Mar 16 2015

Links

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 288...881.

Index entries for primes involving repunits.

Formula

a(n) = A101969(n) + 1.

Mathematica

Do[ If[ PrimeQ[(26*10^n - 71)/9], Print[n]], {n, 10000}]

Crossrefs

Cf. A002275, A101969.

Sequence in context: A152811 A294552 A294170 * A166151 A154149 A354780

Adjacent sequences: A102957 A102958 A102959 * A102961 A102962 A102963

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

Addition of a(12)-a(13) from Kamada data by Robert Price, Dec 13 2010

a(14) from Robert Price, Mar 16 2015

Erroneous zero term deleted by Robert Price, Mar 17 2015

Status

approved