A103075 Numbers n such that 8*10^n + 2*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 4, 5, 8, 10, 22, 223, 254, 350, 379, 401, 436, 1154, 1246, 2053, 2687, 3725, 4271, 13096, 21427, 30266, 36791, 41759

Offset

1,2

Comments

Also numbers n such that (74*10^n+7)/9 is prime.

a(25) > 10^5. - Robert Price, Oct 15 2015

Links

Table of n, a(n) for n=1..24.

Makoto Kamada, Prime numbers of the form 822...223.

Index entries for primes involving repunits.

Formula

a(n) = A101062(n) + 1.

Mathematica

Do[ If[ PrimeQ[(74*10^n + 7)/9], Print[n]], {n, 0, 10000}]

Prog

(PARI) for(n=0, 50000, if(isprime((74*10^n+7)/9), print1(n", "))) \\ Altug Alkan, Oct 15 2015

Crossrefs

Cf. A002275, A101062.

Sequence in context: A018767 A018332 A018257 * A294940 A322125 A174803

Adjacent sequences: A103072 A103073 A103074 * A103076 A103077 A103078

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(20)-a(21) from Kamada data by Robert Price, Dec 14 2010

a(22)-a(24) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Status

approved