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A278442
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Numbers k such that (11*10^k - 179) / 3 is prime.
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0
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2, 3, 4, 5, 7, 14, 16, 47, 68, 103, 127, 341, 523, 562, 1259, 2206, 3164, 3335, 5450, 7700, 7822, 8902, 23237, 36431, 39874, 123899, 129239
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OFFSET
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1,1
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COMMENTS
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For k>1, numbers such that the digit 3 followed by k-2 occurrences of the digit 6 followed by the digits 07 is prime (see Example section).
a(28) > 2*10^5.
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LINKS
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EXAMPLE
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4 is in this sequence because (11*10^4 - 179) / 3 = 36607 is prime.
Initial terms and primes associated:
a(1) = 2, 307;
a(2) = 3, 3607;
a(3) = 4, 36607;
a(4) = 5, 366607;
a(5) = 7, 36666607; etc.
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MATHEMATICA
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Select[Range[2, 100000], PrimeQ[(11*10^# - 179) / 3] &]
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PROG
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(Magma) [n: n in [2..400] | IsPrime((11*10^n-179) div 3)]; // Vincenzo Librandi, Nov 23 2016
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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