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A294230
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Numbers k such that (55*10^k + 377)/9 is prime.
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0
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1, 2, 4, 20, 40, 61, 62, 82, 169, 172, 214, 874, 1520, 1652, 2185, 3221, 4012, 4669, 13165, 18922, 91142, 106222
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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 6 followed by k-2 occurrences of the digit 1 followed by the digits 53 is prime (see Example section).
a(23) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (55*10^2 + 377)/9 = 653 is prime.
Initial terms and primes associated:
a(1) = 1, 103;
a(2) = 2, 653;
a(3) = 4, 61153;
a(4) = 20, 611111111111111111153;
a(5) = 40, 61111111111111111111111111111111111111153; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(55*10^# + 377)/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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EXTENSIONS
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STATUS
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approved
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