A102988 Numbers n such that 4*10^n + 3*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 4, 7, 10, 12, 20, 24, 30, 42, 62, 188, 304, 340, 715, 804, 1040, 1887, 2079, 2120, 2260, 2423, 3319, 5598, 6072, 22048, 25713, 28644, 43353

Offset

1,2

Comments

Also numbers n such that (13*10^n-7)/3 is prime.

a(30) > 10^5. - Robert Price, Mar 30 2015

Links

Table of n, a(n) for n=1..29.

Makoto Kamada, Prime numbers of the form 433...331.

Index entries for primes involving repunits.

Formula

a(n) = A101723(n) + 1.

Mathematica

Do[ If[ PrimeQ[(13*10^n - 7)/3], Print[n]], {n, 1, 10000}]

Crossrefs

Cf. A002275, A101723.

Sequence in context: A007087 A101359 A007303 * A080137 A102933 A122019

Adjacent sequences: A102985 A102986 A102987 * A102989 A102990 A102991

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 17 2005

Extensions

Addition of a(26)-a(28) from Kamada data by Robert Price, Dec 08 2010

a(29) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013

Status

approved