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A287684 Numbers k such that 9*10^k - 23 is prime. 0
1, 2, 4, 13, 16, 19, 25, 44, 55, 64, 69, 183, 241, 290, 345, 398, 410, 423, 860, 1287, 2398, 2553, 3109 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
For k>1, numbers such that the digit 8 followed by k-2 occurrences of the digit 9 followed by the digits 77 is prime (see Example section).
a(24) > 2*10^5.
LINKS
Makoto Kamada, Search for 89w77.
EXAMPLE
4 is in this sequence because 9*10^4 - 23 = 89977 is prime.
Initial terms and primes associated:
a(1) = 1, 67;
a(2) = 2, 877;
a(3) = 4, 89977;
a(4) = 13, 89999999999977;
a(5) = 16, 89999999999999977; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[9*10^# - 23] &]
CROSSREFS
Sequence in context: A024580 A074097 A276481 * A033628 A077319 A291901
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, May 29 2017
STATUS
approved

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Last modified March 28 14:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)