A102981 Numbers n such that 4*10^n + R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 4, 5, 13, 31, 55, 58, 59, 61, 79, 91, 103, 121, 196, 229, 9439, 13051, 22960, 31297

Offset

1,2

Comments

Also numbers n such that (37*10^n+17)/9 is prime.

a(20) > 10^5. - Robert Price, May 08 2015

Links

Table of n, a(n) for n=1..19.

Makoto Kamada, Prime numbers of the form 411...113.

Index entries for primes involving repunits.

Formula

a(n) = A101716(n) + 1.

Mathematica

Do[ If[ PrimeQ[(37*10^n + 17)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101716.

Sequence in context: A304599 A071341 A272898 * A257487 A249394 A295278

Adjacent sequences: A102978 A102979 A102980 * A102982 A102983 A102984

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 21 2004

Extensions

Addition of a(17)-a(18) from Kamada data by Robert Price, Dec 10 2010

a(19) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Status

approved