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A280205
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Numbers k such that (16*10^k + 197) / 3 is prime.
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0
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0, 2, 3, 5, 8, 10, 111, 114, 456, 1158, 1241, 1462, 1736, 1827, 2523, 2812, 3305, 5392, 5897, 6174, 13683, 17088, 23771, 28448, 127259, 142058, 164122
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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 5 followed by k-2 occurrences of the digit 3 followed by the digits 99 is prime (see Example section).
a(28) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (16*10^3 + 197) / 3 = 5399 is prime.
Initial terms and primes associated:
a(1) = 0, 71;
a(2) = 2, 599;
a(3) = 3, 5399;
a(4) = 5, 533399;
a(5) = 8, 533333399; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(16*10^# + 197) / 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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EXTENSIONS
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STATUS
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approved
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