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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 (list; graph; refs; listen; history; text; internal format)
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 A089416 A056817

Adjacent sequences:  A256567 A256568 A256569 * A256571 A256572 A256573

KEYWORD

more,hard,nonn

AUTHOR

Robert Price, Apr 10 2015

STATUS

approved

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Last modified August 9 23:26 EDT 2020. Contains 336335 sequences. (Running on oeis4.)