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A280060
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Numbers k such that (2*10^k + 49)/3 is prime.
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0
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0, 1, 2, 3, 5, 6, 7, 8, 13, 21, 22, 25, 26, 38, 200, 395, 442, 561, 908, 1295, 5541, 7795, 8600, 19157, 22536, 45636
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OFFSET
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1,3
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COMMENTS
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For k > 1, numbers k such that k-2 occurrences of the digit 6 followed by the digits 83 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 (2*10^3 + 49) / 3 = 683 is prime.
Initial terms and associated primes:
a(1) = 0, 17;
a(2) = 1, 23;
a(3) = 2, 83;
a(4) = 3, 683;
a(5) = 5, 66683; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(2*10^# + 49) / 3] &]
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PROG
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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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