A103032 Numbers n such that 6*10^n + 3*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 4, 7, 18, 19, 23, 24, 34, 41, 56, 64, 84, 149, 272, 755, 1272, 2398, 2686, 4800, 5198, 6217, 8737, 12388, 12391, 19702, 42404

Offset

1,2

Comments

Also numbers n such that (19*10^n-7)/3 is prime.

a(28) > 10^5. - Robert Price, Sep 10 2015

Links

Table of n, a(n) for n=1..27.

Makoto Kamada, Prime numbers of the form 633...331.

Index entries for primes involving repunits.

Formula

a(n) = A101525(n) + 1.

Mathematica

Do[ If[ PrimeQ[(19*10^n - 7)/3], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101525.

Sequence in context: A076894 A047871 A290877 * A215649 A259351 A300913

Adjacent sequences: A103029 A103030 A103031 * A103033 A103034 A103035

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

Addition of a(24)-a(26) from Kamada data by Robert Price, Dec 09 2010

a(27) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Status

approved