A256570 Numbers k such that 3*R_k + 10 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 2, 4, 5, 11, 16, 22, 24, 110, 232, 557, 566, 888, 1946, 2610, 3302, 10214, 41756, 89160, 120782

Offset

1,2

Comments

Also, numbers k such that (10^k + 29)/3 is prime.

Terms from Kamada data. Note Kamada does not recognize k=1 as 13 is a degenerate case of form AAA..ABA.

a(21) > 2.5*10^5.

Links

Table of n, a(n) for n=1..20.

Makoto Kamada, Near-repdigit numbers of the form AA...AABA.

Makoto Kamada, Prime numbers of the form 33...3343.

Index entries for primes involving repunits.

Example

For k=4, 3*R_4 + 10 = 3333 + 10 = 3343 which is prime.

Mathematica

Select[Range[0, 250000], PrimeQ[(10^# + 29)/3] &]

Prog

(Magma) [n: n in [0..400] | IsPrime((10^n+29) div 3)]; // Vincenzo Librandi, Apr 11 2015

Crossrefs

Cf. A002275.

Sequence in context: A113733 A294434 A191289 * A284427 A366702 A089416

Adjacent sequences: A256567 A256568 A256569 * A256571 A256572 A256573

Keyword

more,hard,nonn

Author

Robert Price, Apr 10 2015

Status

approved