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A281828 Numbers k such that 7*10^k - 89 is prime. 0
3, 4, 6, 7, 12, 13, 23, 28, 42, 51, 66, 247, 291, 623, 3429, 3892, 4416, 7366, 7991, 8737, 10151, 10209, 40129, 41604, 50818, 68088 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 9 followed by the digits 11 is prime (see Example section).
a(27) > 2*10^5.
LINKS
Makoto Kamada, Search for 69w11.
EXAMPLE
4 is in this sequence because 7*10^4 - 89 = 69911 is prime.
Initial terms and primes associated:
a(1) = 3, 6911;
a(2) = 4, 69911;
a(3) = 6, 6999911;
a(4) = 7, 69999911;
a(5) = 12, 6999999999911; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[7*10^# - 89] &]
CROSSREFS
Sequence in context: A033162 A105133 A211384 * A002982 A290432 A276783
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 31 2017
STATUS
approved

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Last modified March 29 06:57 EDT 2024. Contains 371265 sequences. (Running on oeis4.)