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URL: https://oeis.org/A288151

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A288151
Numbers k such that 98*10^k - 3 is prime.
0
1, 5, 7, 8, 13, 20, 33, 39, 43, 51, 91, 113, 119, 132, 208, 411, 525, 581, 931, 1552, 4829, 17537, 40301, 43429
OFFSET
1,2
COMMENTS
For k > 0, numbers k such that the digits 97 followed by k-1 occurrences of the digit 9 followed by the digit 7 is prime (see Example section).
a(25) > 2*10^5.
EXAMPLE
5 is in this sequence because 98*10^5 - 3 = 9799997 is prime.
Initial terms and associated primes:
a(1) = 1, 977;
a(2) = 5, 9799997;
a(3) = 7, 979999997;
a(4) = 8, 9799999997;
a(5) = 13, 979999999999997; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[98*10^# - 3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jun 05 2017
STATUS
approved