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A283246 Numbers k such that (17*10^k - 179)/9 is prime. 0
4, 5, 10, 13, 16, 106, 130, 148, 880, 1261, 2560, 2629, 3730, 5284, 7411, 8255, 9091, 9490, 10171, 14033, 25618, 39382, 47452 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 8 followed by the digits 69 is prime (see Example section).
a(24) > 2*10^5.
LINKS
Makoto Kamada, Search for 18w69.
EXAMPLE
5 is in this sequence because (17*10^5 - 179)/9 = 188869 is prime.
Initial terms and associated primes:
a(1) = 4, 18869;
a(2) = 5, 188869;
a(3) = 10, 18888888869;
a(4) = 13, 18888888888869;
a(5) = 16, 18888888888888869; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[(17*10^# - 179)/9] &]
PROG
(PARI) is(n)=isprime((17*10^k - 179)/9) \\ Charles R Greathouse IV, Mar 05 2017
CROSSREFS
Sequence in context: A222353 A094415 A114517 * A236283 A357865 A366864
KEYWORD
nonn,more,hard,changed
AUTHOR
Robert Price, Mar 05 2017
STATUS
approved

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Last modified June 21 03:48 EDT 2024. Contains 373535 sequences. (Running on oeis4.)