A102943 Numbers k such that 10^k + 7*R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 2, 8, 10, 25, 50, 76, 104, 4406, 8935, 26000, 31652

Offset

1,2

Comments

Also numbers k such that (16*10^k + 11)/9 is prime.

a(13) > 10^5. - Robert Price, Feb 07 2015

Links

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

Makoto Kamada, Prime numbers of the form 177...779.

Index entries for primes involving repunits.

Formula

a(n) = A102028(n) - 1.

Mathematica

Do[ If[ PrimeQ[(16*10^n + 11)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A102028.

Sequence in context: A209449 A002510 A247592 * A327988 A062880 A066707

Adjacent sequences: A102940 A102941 A102942 * A102944 A102945 A102946

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 16 2004

Extensions

Addition of a(11) from Kamada data by Robert Price, Dec 13 2010

a(12) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Status

approved