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A291923
Numbers k such that (482*10^k - 41)/9 is prime.
0
2, 3, 5, 14, 17, 23, 33, 38, 71, 242, 359, 536, 579, 629, 758, 2957, 3797, 12609, 16184, 21285, 41151
OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digits 53 followed by k-1 occurrences of the digit 5 followed by the digit 1 is prime (see Example section).
a(22) > 2*10^5.
EXAMPLE
3 is in this sequence because (482*10^3 - 41)/9 = 53551 is prime.
Initial terms and associated primes:
a(1) = 2, 5351;
a(2) = 3, 53551;
a(3) = 5, 5355551;
a(4) = 14, 5355555555555551;
a(5) = 17, 5355555555555555551; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(482*10^# - 41)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Sep 05 2017
STATUS
approved