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A280942
Numbers k such that (29*10^k - 77)/3 is prime.
0
1, 2, 12, 14, 31, 32, 42, 44, 69, 134, 146, 164, 560, 846, 1410, 1416, 1962, 1995, 2546, 3506, 4334, 7035, 12901, 20137, 42206, 45890, 58417, 106620, 126928, 197629
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 6 followed by the digits 41 is prime (see Example section).
a(31) > 2*10^5.
EXAMPLE
2 is in this sequence because (29*10^2 - 77) / 3 = 941 is prime.
Initial terms and associated primes:
a(1) = 1, 71;
a(2) = 2, 941;
a(3) = 12, 9666666666641;
a(4) = 14, 966666666666641;
a(5) = 32, 96666666666666666666666666666641; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(29*10^# - 77) / 3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 11 2017
EXTENSIONS
a(28)-a(30) from Robert Price, Jan 31 2020
STATUS
approved