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A294913
Numbers k such that (89*10^k - 539)/9 is prime.
0
2, 3, 5, 8, 9, 18, 20, 26, 111, 141, 162, 236, 312, 383, 2093, 3926, 3981, 4935, 17126, 32070, 64608, 86802
OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 8 followed by the digits 29 is prime (see Example section).
a(23) > 2*10^5.
EXAMPLE
2 is in this sequence because (89*10^2 - 539)/9 = 929 is prime.
Initial terms and associated primes:
a(1) = 2, 929;
a(2) = 3, 9829;
a(3) = 5, 988829;
a(4) = 8, 988888829;
a(5) = 9, 9888888829; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(89*10^# - 539)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 10 2017
STATUS
approved