A103102 Numbers n such that 9*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 7, 67, 127, 2107, 10003, 13741, 41523

Offset

1,3

Comments

Also numbers n such that (86*10^n+13)/9 is prime.

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

Links

Table of n, a(n) for n=1..9.

Makoto Kamada, Prime numbers of the form 955...557.

Index entries for primes involving repunits.

Formula

a(n) = A101011(n-1) + 1, for n>1.

Mathematica

Do[ If[ PrimeQ[(86*10^n + 13)/9], Print[n]], {n, 0, 10000}]

Prog

(PARI) is(n)=isprime(9*10^n + 5*((10^n-1)/9) + 2) \\ Anders Hellström, Nov 10 2015

Crossrefs

Cf. A002275, A101011.

Sequence in context: A261184 A142786 A139783 * A139910 A250227 A250275

Adjacent sequences: A103099 A103100 A103101 * A103103 A103104 A103105

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(7)-a(8) from Kamada data by Robert Price, Dec 14 2010

a(9) from Erik Branger May 01 2013 by Ray Chandler, Aug 17 2013

Inserted a(1)=0 by Robert Price, Nov 10 2015

Status

approved