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A281929
Numbers k such that (19*10^k + 119)/3 is prime.
0
1, 2, 3, 8, 10, 12, 67, 188, 192, 228, 363, 372, 658, 1748, 1866, 2539, 7897, 10399, 10519, 12872, 14796, 16773, 24736, 30456, 46425, 57316, 65572, 75338
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 3 followed by the digits 73 is prime (see Example section).
a(29) > 2*10^5.
EXAMPLE
3 is in this sequence because (19*10^3 + 119)/3 = 6373 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 2, 673;
a(3) = 3, 6373;
a(4) = 8, 633333373;
a(5) = 10, 63333333373; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(19*10^# + 119)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 11 2017
STATUS
approved