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URL: https://oeis.org/A293759

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A293759
Numbers k such that (35*10^k - 197)/9 is prime.
0
1, 2, 4, 7, 8, 19, 26, 28, 38, 43, 67, 331, 359, 832, 907, 1880, 2359, 4301, 5896, 6187, 37154, 40411, 59584
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 8 followed by the digits 67 is prime (see Example section).
a(24) > 2*10^5.
EXAMPLE
2 is in this sequence because (35*10^2 - 197)/9 = 367 is prime.
Initial terms and associated primes:
a(1) = 1, 17;
a(2) = 2, 367;
a(3) = 4, 38867;
a(4) = 7, 38888867;
a(5) = 8, 388888867; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(35*10^# - 197)/9] &]
PROG
(Magma) [n: n in [1..400] |IsPrime((35*10^n - 197) div 9)]; // Vincenzo Librandi, Oct 16 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 15 2017
EXTENSIONS
Comments, Link and Example corrected by Robert Price, Jun 11 2018
STATUS
approved