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A026238
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a(n) = j if n is the j-th prime, else a(n) = k if n is the k-th composite.
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7
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1, 2, 1, 3, 2, 4, 3, 4, 5, 5, 6, 6, 7, 8, 9, 7, 10, 8, 11, 12, 13, 9, 14, 15, 16, 17, 18, 10, 19, 11, 20, 21, 22, 23, 24, 12, 25, 26, 27, 13, 28, 14, 29, 30, 31, 15, 32, 33, 34, 35, 36, 16, 37, 38, 39, 40, 41, 17, 42, 18, 43, 44, 45, 46, 47, 19
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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2,2
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LINKS
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MATHEMATICA
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Table[If[PrimeQ[n], PrimePi[n], n-1-PrimePi[n]], {n, 2, 70}] (* Harvey P. Dale, Jun 06 2017 *)
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PROG
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(Haskell)
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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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