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A199716
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Numbers k such that 6k-5 and 6k-1 are both composite.
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0
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16, 20, 21, 35, 37, 50, 51, 54, 55, 61, 66, 68, 76, 79, 81, 83, 86, 89, 90, 105, 112, 115, 118, 121, 125, 128, 130, 131, 134, 141, 142, 145, 146, 149, 150, 151, 153, 156, 160, 161, 165, 168, 180, 181, 186, 190, 191, 195, 200, 202, 208, 211, 212, 219, 223
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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Select[Range[223], ! PrimeQ[6#-5] && ! PrimeQ[6#-1] &] (* T. D. Noe, Nov 09 2011 *)
Select[Range[250], AllTrue[6#+{-5, -1}, CompositeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Oct 11 2018 *)
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PROG
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(Magma) [ n: n in [1..223] | not IsPrime(6*n-5) and not IsPrime(6*n-1) ]; // Bruno Berselli, Nov 09 2011
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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