A103052 Numbers k such that 7*10^k + 2*R_k - 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 4, 16, 25, 29, 41, 47, 88, 1132, 1570, 3985, 10609, 12175, 29369

Offset

1,2

Comments

Also numbers k such that (65*10^k-11)/9 is prime.

a(15) > 10^5. - Robert Price, Sep 23 2015

Links

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

Makoto Kamada, Prime numbers of the form 722...221.

Index entries for primes involving repunits.

Formula

a(n) = A101133(n) + 1.

Mathematica

Do[ If[ PrimeQ[(65*10^n - 11)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101133.

Sequence in context: A305884 A239522 A281990 * A228004 A269157 A343726

Adjacent sequences: A103049 A103050 A103051 * A103053 A103054 A103055

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(12)-a(14) from Kamada data by Robert Price, Dec 14 2010

Status

approved