A102961 Numbers k such that 2*10^k + 8*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 2, 7, 28, 73, 295, 494, 598, 2600, 3730, 7549, 15865

Offset

1,2

Comments

Also numbers k such that (26*10^k-53)/9 is prime.

a(13) > 10^5. - Robert Price, Apr 18 2014

Links

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

Makoto Kamada, Prime numbers of the form 288...883.

Index entries for primes involving repunits.

Formula

a(n) = A101970(n) + 1.

Mathematica

Do[ If[ PrimeQ[(26*10^k - 53)/9], Print[k]], {k, 1, 10000}]

Crossrefs

Cf. A002275, A101970.

Sequence in context: A294128 A099815 A123363 * A155581 A349329 A048504

Adjacent sequences: A102958 A102959 A102960 * A102962 A102963 A102964

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

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

0 removed by Georg Fischer, Jan 03 2021

Status

approved