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A291867
Numbers k such that (17*10^k - 41)/3 is prime.
0
1, 3, 5, 7, 13, 18, 45, 73, 165, 174, 298, 502, 563, 901, 1033, 1164, 1181, 2040, 4165, 20389, 23608, 34542, 88761
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 6 followed by the digits 53 is prime (see Example section).
a(24) > 2*10^5.
EXAMPLE
3 is in this sequence because (17*10^3 - 41)/3 = 5653 is prime.
Initial terms and associated primes:
a(1) = 1, 43;
a(2) = 3, 5653;
a(3) = 5, 566653;
a(4) = 7, 56666653;
a(5) = 13, 56666666666653; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(17*10^# - 41)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Sep 04 2017
STATUS
approved