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A309774
Numbers k such that 5*10^k + 11 is prime.
0
1, 3, 6, 35, 51, 84, 123, 1589, 1591, 4911, 6221, 48645, 78504, 107355
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 11 is prime (see Example section).
a(15) > 2*10^5.
EXAMPLE
6 is in this sequence because 5*10^4 + 11 = 5000011 is prime.
Initial terms and associated primes:
a(1) = 1, 61;
a(2) = 3, 5011;
a(3) = 6, 5000011;
a(4) = 35, 500000000000000000000000000000000011; etc.
MATHEMATICA
Select[Range[0, 200000], PrimeQ[5*10^# + 11] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Aug 16 2019
STATUS
approved