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A273907
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Numbers k such that 2*10^k - 87 is prime.
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0
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2, 3, 4, 9, 10, 13, 15, 24, 26, 38, 39, 42, 433, 489, 495, 513, 597, 829, 2019, 2738, 3096, 3691, 5437, 7537, 8536, 34125, 40105, 41790, 52713, 104811, 173809, 175860
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OFFSET
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1,1
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COMMENTS
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For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 9 followed by the digits 13 is prime (see Example section).
a(33) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because 2*10^3 - 87 = 1913 is prime.
Initial terms and associated primes:
a(1) = 2, 113;
a(2) = 3, 1913;
a(3) = 4, 19913;
a(4) = 9, 1999999913;
a(5) = 10, 19999999913, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[2*10^# - 87] &]
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PROG
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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