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A026233
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a(n) = j if n is the j-th prime, else a(n) = k if n is the k-th nonprime.
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1
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1, 1, 2, 2, 3, 3, 4, 4, 5, 6, 5, 7, 6, 8, 9, 10, 7, 11, 8, 12, 13, 14, 9, 15, 16, 17, 18, 19, 10, 20, 11, 21, 22, 23, 24, 25, 12, 26, 27, 28, 13, 29, 14, 30, 31, 32, 15, 33, 34, 35, 36, 37, 16, 38, 39, 40, 41, 42, 17, 43, 18, 44, 45, 46, 47, 48
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Each n occurs at two positions, the distances between them are: 1, 1, 1, 1, 2, 3, 5, 5, 8, 13, 13, 17, 20, 21, 23, 28, 33, 34, 39, 41, 41, ... - Zak Seidov, Mar 06 2011.
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MATHEMATICA
| m=100; pr=Prime[Range[m]]; npr=Select[Range[m], !PrimeQ[#]&];
a[n_]:=If[PrimeQ[n], PrimePi[n], Position[npr, n][[1, 1]]]; Table[a[n], {n, m}] (* Zak Seidov Mar 05 2011 *) s=Range[500]; Do[s=Insert[s, n, Prime[n]], {n, 100}]; s (* Zak Seidov Mar 05 2011 *)
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CROSSREFS
| Sequence in context: A079685 A112409 A026261 * A147954 A194204 A100679
Adjacent sequences: A026230 A026231 A026232 * A026234 A026235 A026236
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KEYWORD
| nonn
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AUTHOR
| Clark Kimberling (ck6(AT)evansville.edu)
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