This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A080999 #4 Mar 30 2012 17:27:18 %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, %T A080999 168,33,180,81,75,195,112,240,65,37,360,105,117,189,168,99,45,243,260, %U A080999 125,420,195,111,200,520,315,351,567,273,57,432,135,61,165,256,900,189,375 %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. %K A080999 nonn %O A080999 1,2 %A A080999 _Matthew Vandermast_, Mar 02 2003