

A256570


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


0



1, 2, 4, 5, 11, 16, 22, 24, 110, 232, 557, 566, 888, 1946, 2610, 3302, 10214, 41756, 89160, 120782
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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, Nearrepdigit 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 A089416 A056817
Adjacent sequences: A256567 A256568 A256569 * A256571 A256572 A256573


KEYWORD

more,hard,nonn


AUTHOR

Robert Price, Apr 10 2015


STATUS

approved



