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A100802
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a(n) = least k >= 0 such that (n+k)/2 is prime.
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2
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4, 3, 2, 1, 0, 1, 0, 3, 2, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 3, 2, 1, 0, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 11, 10, 9, 8, 7, 6, 5
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OFFSET
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0,1
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COMMENTS
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If a(n) = k is nonzero then a(n+1) = k-1. a(2p) = 0 for p prime.
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LINKS
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MATHEMATICA
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a = {}; Do[k = 0; While[ ! PrimeQ[(n + k)/2], k++ ]; AppendTo[a, k]; , {n, 0, 120}]; a (* Ray Chandler, Jan 19 2005 *)
lk[n_]:=Module[{k=If[EvenQ[n], 0, 1]}, While[!PrimeQ[(n+k)/2], k=k+2]; k]; Array[lk, 120, 0] (* Harvey P. Dale, Nov 25 2016 *)
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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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EXTENSIONS
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STATUS
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approved
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