A103030 Numbers n such that 6*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 3, 7, 16, 39, 229, 352, 433, 766, 2887, 2976, 10836, 15097

Offset

1,3

Comments

Also numbers n such that (56*10^n-11)/9 is prime.

a(15) > 10^5. - Robert Price, Sep 08 2015

Links

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 622...221.

Index entries for primes involving repunits.

Formula

a(n) = A101522(n-1) + 1.

Example

For n=0, (56*10^n-11)/9 = 5 which is prime, so 0 is in the sequence.

Mathematica

Do[ If[ PrimeQ[(56*10^n - 11)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101522.

Sequence in context: A271788 A103439 A147321 * A263316 A001698 A261236

Adjacent sequences: A103027 A103028 A103029 * A103031 A103032 A103033

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

Addition of a(13)-a(14) from Kamada data by Robert Price, Dec 13 2010

Inserted a(1)=0 by Robert Price, Sep 08 2015

Status

approved