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A286177
Numbers k such that (17*10^k - 47)/3 is prime.
0
1, 3, 8, 9, 14, 17, 29, 43, 48, 72, 78, 132, 312, 894, 968, 5030, 5108, 9008, 11989, 12903, 26767, 28159, 30564, 39619, 44250, 54537, 77427
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 6 followed by the digits 51 is prime (see Example section).
a(28) > 2*10^5.
EXAMPLE
3 is in this sequence because (17*10^3 - 47)/3 = 5651 is prime.
Initial terms and associated primes:
a(1) = 1, 41;
a(2) = 3, 5651;
a(3) = 8, 566666651;
a(4) = 9, 5666666651;
a(5) = 14, 566666666666651; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(17*10^# - 47)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, May 03 2017
STATUS
approved