A102957 Numbers n such that 2*10^n + 6*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 2, 4, 7, 14, 20, 39, 102, 156, 457, 1190, 2308, 5870, 8314, 9703, 12828, 14959, 17995, 19730, 26480, 31440

Offset

1,3

Comments

Also numbers n such that (8*10^n+7)/3 is prime.

Links

Table of n, a(n) for n=1..22.

Makoto Kamada, Prime numbers of the form 266...669.

Index entries for primes involving repunits.

Formula

a(n) = A101965(n-1) + 1.

Mathematica

Do[ If[ PrimeQ[(8*10^n + 7)/3], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101965.

Sequence in context: A108329 A057264 A045514 * A216898 A176450 A263345

Adjacent sequences: A102954 A102955 A102956 * A102958 A102959 A102960

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

Addition of a(17)-a(21) from Kamada data by Robert Price, Dec 10 2010

0 added by Arkadiusz Wesolowski, Mar 10 2011

a(22) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Status

approved