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A284595 Numbers k such that (349*10^k - 7)/9 is prime. 0
2, 12, 21, 30, 63, 86, 140, 173, 308, 318, 402, 410, 441, 492, 2186, 4580, 5100, 5208, 5810, 7476, 21677, 31766, 45357, 48036, 66720 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digits 38 followed by k occurrences of the digit 7 is prime (see Example section).
a(26) > 2*10^5.
LINKS
Makoto Kamada, Search for 387w.
EXAMPLE
2 is in this sequence because (349*10^2 - 7)/9 = 3877 is prime.
Initial terms and associated primes:
a(1) = 2, 3877;
a(2) = 12, 38777777777777;
a(3) = 21, 38777777777777777777777;
a(4) = 30, 38777777777777777777777777777777;
a(5) = 63, 38777777777777777777777777777777777777777777777777777777777777777; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(349*10^# - 7)/9] &]
CROSSREFS
Sequence in context: A304813 A279424 A073041 * A053898 A058413 A053890
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Mar 29 2017
STATUS
approved

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Last modified July 15 11:01 EDT 2024. Contains 374332 sequences. (Running on oeis4.)