Search: id:A080999
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%I A080999
%S A080999 1,3,5,8,15,9,20,40,27,13,21,45,39,63,48,72,100,21,135,25,65,104,63,168,
%T A080999 33,180,81,75,195,112,240,65,37,360,105,117,189,168,99,45,243,260,125,
%U A080999 420,195,111,200,520,315,351,567,273,57,432,135,61,165,256,900,189,375
%N A080999 Centrality of A080997(n) = a(n)/(A080997(n))^2.
%C A080999 A permutation of sequence A018804, which gives the sum of gcd (k,n) for 
               1 <= k <= n.
%F A080999 The multiplicative formula for the numerator in a positive integer's 
               centrality fraction is: for prime p, a(p^e)= p^(e-1)*((p-1)e+p) (cf. 
               A018804). Dividing by the square of the integer gives the integer's 
               centrality, which is defined to be the average fraction of the integer 
               that it shares with the other integers as a gcd; see A080997 for 
               other interpretations. This sequence gives the unreduced centrality 
               numerators for A080997(n), where A080997 is the sequence of positive 
               integers in nonincreasing order of their centrality.
%Y A080999 Cf. A080997, A080998 for centrality rankings of the positive integers.
%Y A080999 Sequence in context: A072655 A108301 A095290 this_sequence A077579 A076797 
               A052977
%Y A080999 Adjacent sequences: A080996 A080997 A080998 this_sequence A081000 A081001 
               A081002
%K A080999 nonn
%O A080999 1,2
%A A080999 Matthew Vandermast (ghodges14(AT)comcast.net), Mar 02 2003

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