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A288824
Numbers k such that (26*10^k + 61)/3 is prime.
0
0, 1, 2, 8, 10, 17, 18, 30, 37, 42, 47, 100, 286, 287, 440, 1074, 1124, 2298, 2879, 4948, 4950, 12730, 17429, 31768, 47726, 64220, 80200, 127240
OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 87 is prime (see Example section).
a(29) > 2*10^5.
EXAMPLE
2 is in this sequence because (26*10^2 + 61)/3 = 887 is prime.
Initial terms and associated primes:
a(1) = 0, 29;
a(2) = 1, 107;
a(3) = 2, 887;
a(4) = 8, 866666687;
a(5) = 10, 86666666687; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(26*10^# + 61)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jun 17 2017
EXTENSIONS
a(28) from Robert Price, Oct 13 2019
STATUS
approved