A103055 Numbers n such that 7*10^n + 3*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 3, 4, 5, 6, 9, 12, 31, 59, 69, 74, 287, 489, 592, 634, 1089, 1607, 3141, 5962, 6267, 9678, 11431, 12927, 32189, 38700, 53033, 83525, 185950

Offset

1,2

Comments

Also numbers n such that (22*10^n-7)/3 is prime.

a(29) > 3*10^5 Robert Price, Jun 01 2023

Links

Table of n, a(n) for n=1..28.

Makoto Kamada, Prime numbers of the form 733...331.

Index entries for primes involving repunits.

Formula

a(n) = A101137(n) + 1.

Mathematica

Do[ If[ PrimeQ[(22*10^n - 7)/3], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101137.

Sequence in context: A088875 A022884 A105857 * A128995 A293306 A014101

Adjacent sequences: A103052 A103053 A103054 * A103056 A103057 A103058

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(22)-a(23) Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(24)-a(25) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(26)-a(27) from Erik Branger Sep 08 2014 by Ray Chandler, Apr 23 2015

a(28) from Robert Price, Jun 01 2023

Status

approved