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 A081000 #5 Mar 30 2012 17:27:18 %S A081000 1,2,3,4,6,8,10,12,14,15,16,18,20,21,24,27,28,30,32,36,40,42,44,45,48, %T A081000 50,52,54,56,60,63,64,66,68,70,72,75,76,78,80,84,88,90,96,98,99,100, %U A081000 102,104,105,108,110,112,114,117,120 %N A081000 n is a member if and only if it ranks among top n positive integers in centrality (cf. A080997 for fuller description of this concept). %C A081000 1, 2, 3, 4, 21 and 27 are currently the only known examples of n that rank exactly n-th in centrality; it is not known whether there are others. %F A081000 The formula for the centrality of an integer is A018804(n)/n^2; see also A080997. %Y A081000 Cf. A080997, A080998, also A081029, the highly central integers (a subset of this sequence). Complement is A081001. %K A081000 nonn %O A081000 1,2 %A A081000 _Matthew Vandermast_, Mar 02 2003