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A294681 Numbers k such that (871*10^k - 7)/9 is prime. 0
1, 2, 7, 26, 28, 31, 38, 47, 59, 226, 233, 656, 752, 1073, 1808, 3646, 4252, 5246, 24686, 37952, 59599 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Numbers k such that the digits 96 followed by k occurrences of the digit 7 is prime (see Example section).
a(22) > 2*10^5.
LINKS
Makoto Kamada, Search for 967w.
EXAMPLE
2 is in this sequence because (871*10^2 - 7)/9 = 9677 is prime.
Initial terms and associated primes:
a(1) = 1, 967;
a(2) = 2, 9677;
a(3) = 7, 967777777;
a(4) = 26, 9677777777777777777777777777;
a(5) = 28, 967777777777777777777777777777; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(871*10^# - 7)/9] &]
CROSSREFS
Sequence in context: A018980 A012990 A137102 * A229241 A335179 A091145
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 06 2017
STATUS
approved

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Last modified July 23 14:37 EDT 2024. Contains 374549 sequences. (Running on oeis4.)