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A046953
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Numbers k such that 6*k - 1 is composite.
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13
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6, 11, 13, 16, 20, 21, 24, 26, 27, 31, 34, 35, 36, 37, 41, 46, 48, 50, 51, 54, 55, 56, 57, 61, 62, 63, 66, 68, 69, 71, 73, 76, 79, 81, 83, 86, 88, 89, 90, 91, 92, 96, 97, 101, 102, 104, 105, 106, 111, 112, 115, 116, 118, 119, 121, 122, 123, 125, 126, 128
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OFFSET
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1,1
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COMMENTS
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These numbers can be written as 6*x*y + x - y for x > 0, y > 0. - Ron R Spencer, Aug 01 2016
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LINKS
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FORMULA
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EXAMPLE
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a(1)=6 because 6*6 - 1 = 35, which is composite.
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MAPLE
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remove(k-> isprime(6*k-1), [$1..130])[]; # Muniru A Asiru, Feb 22 2019
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MATHEMATICA
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PROG
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(Haskell)
a046953 n = a046953_list !! (n-1)
a046953_list = map (`div` 6) $
filter ((== 0) . a010051' . subtract 1) [6, 12..]
(Magma) [n: n in [1..200] | not IsPrime(6*n-1)]; // G. C. Greubel, Feb 21 2019
(Sage) [n for n in (1..200) if not is_prime(6*n-1)] # G. C. Greubel, Feb 21 2019
(GAP) Filtered([1..200], k-> not IsPrime(6*k-1)) # G. C. Greubel, Feb 21 2019
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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