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A284886
Numbers k such that (14*10^k - 101)/3 is prime.
0
1, 2, 4, 6, 14, 20, 305, 470, 507, 1104, 1152, 1725, 1944, 5864, 6785, 7446, 11460, 12412, 16302, 19787, 24029, 27240, 67235, 83471, 89480, 116112
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 6 followed by the digits 33 is prime (see Example section).
a(27) > 2*10^5.
EXAMPLE
4 is in this sequence because (14*10^4 - 101)/3 = 46633 is prime.
Initial terms and associated primes:
a(1) = 1, 13;
a(2) = 2, 433;
a(3) = 4, 46633;
a(4) = 6, 4666633;
a(5) = 14, 466666666666633; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(14*10^# - 101)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 04 2017
EXTENSIONS
a(26) from Robert Price, Feb 23 2019
STATUS
approved