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A257038 Numbers k such that 9*R_(k+2) - 5*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k. 0
3, 192, 1133, 4763, 5812, 48467, 130620, 466002 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Also, numbers k such that 95*10^k - 1 is prime.
Terms from Kamada.
a(9) > 1170000.
LINKS
EXAMPLE
For k=3, 9*R_5 - 5*10^3 = 99999 - 5000 = 94999 which is prime.
MATHEMATICA
Select[Range[0, 1170000], PrimeQ[95*10^#-1 ] &]
PROG
(Magma) [n: n in [0..400] | IsPrime(95*10^n-1)]; // Vincenzo Librandi, Apr 15 2015
CROSSREFS
Cf. A002275.
Sequence in context: A365447 A032594 A159658 * A202109 A230171 A332957
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 14 2015
STATUS
approved

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Last modified July 13 04:46 EDT 2024. Contains 374267 sequences. (Running on oeis4.)