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A281275
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Numbers k such that (19*10^k + 467)/9 is prime.
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0
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1, 2, 4, 7, 8, 14, 19, 34, 40, 55, 178, 251, 314, 410, 982, 1198, 1604, 2486, 2642, 3928, 19231, 24874, 28850, 143963
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OFFSET
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1,2
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COMMENTS
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For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 1 followed by the digits 63 is prime (see Example section).
a(25) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (19*10^2 + 467)/9 = 263 is prime.
Initial terms and associated primes:
a(1) = 1, 73;
a(2) = 2, 263;
a(3) = 4, 21163;
a(4) = 7, 21111163;
a(5) = 8, 211111163; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(19*10^# + 467)/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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