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Search: id:A080998
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| A080998 |
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a(n) is n's rank among the positive integers in terms of centrality -the fraction of n represented by the average gcd of n and the positive integers, or A018804(n)/n^2 (cf. A080997). |
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+0
8
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| 1, 2, 3, 4, 6, 5, 10, 7, 11, 9, 18, 8, 20, 13, 12, 15, 25, 14, 33, 16, 21, 23, 40, 17, 32, 28, 27, 22, 53, 19, 56, 30, 35, 39, 36, 24, 69, 46, 43, 26, 79, 29, 89, 38, 37, 55, 95, 31, 67, 45, 57, 47, 108, 41, 60, 42, 65, 75
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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a(5)=6 because the centrality of 5 is 9/25 (.36), which places it sixth among positive integers in centrality; it ranks behind 1 (whose centrality is 1), 2 (3/4, .75), 3 (5/9, .555...), 4 (1/2, .5) and 6 (5/12, .41666...).
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CROSSREFS
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A080997 gives fuller description of centrality, as well as finite portion of the arrangement of positive integers in order of their centrality. For more about where numbers occur in A080997, see also A081000, A081001, A081028, A081029.
Sequence in context: A075159 A095424 A064275 this_sequence A119629 A014631 A064787
Adjacent sequences: A080995 A080996 A080997 this_sequence A080999 A081000 A081001
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KEYWORD
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nonn
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AUTHOR
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Matthew Vandermast (ghodges14(AT)comcast.net), Mar 02 2003
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