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A256711 Numbers k such that R_k - 10 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 0
3, 8, 12, 17, 86, 146, 1428, 1949, 4809, 16922, 33102, 125792, 211610 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Also, numbers k such that (10^k - 91)/9 is prime.
Terms from Kamada data.
a(14) > 2.5*10^5.
LINKS
EXAMPLE
For k=3, R_3 - 10 = 111 - 10 = 101 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(10^# - 91)/9] &]
PROG
(Magma) [n: n in [0..1400] | IsPrime((10^n-91) div 9)]; // Vincenzo Librandi, Apr 09 2015
CROSSREFS
Cf. A002275.
Sequence in context: A190374 A189758 A190368 * A219635 A063225 A213238
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 08 2015
STATUS
approved

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Last modified May 18 03:36 EDT 2024. Contains 372618 sequences. (Running on oeis4.)