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A290433
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Numbers k such that (85*10^k - 103)/9 is prime.
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0
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1, 3, 4, 16, 28, 45, 46, 67, 93, 130, 265, 321, 376, 717, 934, 1047, 1420, 2547, 5683, 8593, 9445, 31086, 33382, 43089, 76021, 90745
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OFFSET
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1,2
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COMMENTS
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For k > 1, numbers such that the digit 9 followed by k-2 occurrences of the digit 4 followed by the digits 33 is prime (see Example section).
a(27) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (85*10^3 - 103)/9 = 9433 is prime.
Initial terms and primes associated:
a(1) = 1, 83;
a(2) = 3, 9433;
a(3) = 4, 94433;
a(4) = 16, 94444444444444433;
a(5) = 28, 94444444444444444444444444433; etc.
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MATHEMATICA
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Select[Range[1, 100000], PrimeQ[85*10^# - 103)/9] &]
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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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STATUS
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approved
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