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A281144 Numbers k such that (302*10^k + 13)/9 is prime. 0
1, 4, 7, 9, 16, 33, 55, 63, 75, 195, 412, 766, 1083, 1657, 2254, 4972, 10053, 10605, 13413, 18085, 24595, 25161, 36441, 80638, 178369 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
For k>0, numbers such that the digits 33 followed by k-1 occurrences of the digit 5 followed by the digit 7 is prime (see Example section).
a(26) > 2*10^5.
LINKS
Makoto Kamada, Search for 335w7.
EXAMPLE
4 is in this sequence because (302*10^4 + 13)/9 = 335557 is prime.
Initial terms and primes associated:
a(1) = 1, 337;
a(2) = 4, 335557;
a(3) = 7, 335555557;
a(4) = 9, 33555555557;
a(5) = 16, 335555555555555557; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(302*10^# + 13)/9] &]
CROSSREFS
Sequence in context: A010424 A044903 A359016 * A103073 A166742 A346554
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 15 2017
EXTENSIONS
a(25) from Robert Price, Feb 08 2020
STATUS
approved

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Last modified March 29 02:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)