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A286426 Numbers k such that (22*10^k + 71)/3 is prime. 0
0, 1, 2, 6, 20, 23, 86, 146, 167, 340, 472, 500, 898, 907, 936, 1133, 2069, 3166, 4207, 5275, 9700, 20407, 28009, 32923, 53264 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 3 followed by the digits 57 is prime (see Example section).
a(26) > 2*10^5.
LINKS
Makoto Kamada, Search for 73w57.
EXAMPLE
2 is in this sequence because (22*10^2 + 71)/3 = 757 is prime.
Initial terms and associated primes:
a(1) = 0, 31;
a(2) = 1, 97;
a(3) = 2, 757;
a(4) = 6, 7333357;
a(5) = 20, 733333333333333333357; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(22*10^# + 71)/3] &]
CROSSREFS
Sequence in context: A205012 A254120 A356778 * A028689 A156269 A370974
KEYWORD
nonn,more,hard,changed
AUTHOR
Robert Price, May 09 2017
STATUS
approved

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Last modified June 14 10:58 EDT 2024. Contains 373396 sequences. (Running on oeis4.)