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A295324 Numbers k such that (17*10^k - 89)/9 is prime. 0
2, 3, 6, 12, 39, 45, 50, 75, 126, 282, 431, 459, 1557, 2724, 3453, 4058, 15879, 24209, 31844, 61760, 155133 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
For k > 1, numbers such that the digit 1 followed by k-2 occurrences of the digit 8 followed by the digits 79 is prime (see Example section).
a(22) > 2*10^5.
LINKS
Makoto Kamada, Search for 18w79
EXAMPLE
2 is in this sequence because (17*10^2 - 89)/9 = 179 is prime.
Initial terms and primes associated:
a(1) = 2, 179;
a(2) = 3, 1879;
a(3) = 6, 1888879;
a(4) = 12, 1888888888879;
a(5) = 39, 1888888888888888888888888888888888888879; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(17*10^# - 89)/9] &]
PROG
(PARI) isok(k) = isprime((17*10^k - 89)/9); \\ Michel Marcus, Nov 20 2017
CROSSREFS
Sequence in context: A102970 A144771 A187013 * A054049 A276690 A175281
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 19 2017
EXTENSIONS
a(21) from Robert Price, Jul 23 2018
STATUS
approved

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Last modified March 28 16:58 EDT 2024. Contains 371254 sequences. (Running on oeis4.)