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 A287009 #17 Feb 16 2025 08:33:46 %S A287009 1,1,2,6,20,109,820,10618,244536,10740858,905808814 %N A287009 Number of connected simple weakly perfect graphs on n vertices. %C A287009 First differs from A243252 (connected simple graphs whose fractional number equals its chromatic number) at a(8). The three (connected) 8-node graphs that have equal chromatic and fractional chromatic numbers but are not weakly perfect are the 4-antiprism graph and 50- and 84-Johnson solid skeleton graphs, all of which have clique number 3 but chromatic and fractional chromatic number 4. %H A287009 F. Hüffner, <a href="https://github.com/falk-hueffner/tinygraph">tinygraph</a>, software for generating integer sequences based on graph properties, version 4361e42 %H A287009 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ConnectedGraph.html">Connected Graph</a> %H A287009 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/WeaklyPerfectGraph.html">Weakly Perfect Graph</a> %F A287009 a(n) = A198634(n) - A287023(n). %Y A287009 Cf. A198634 (not necessarily connected weakly perfect simple graphs on n nodes). %Y A287009 Cf. A287023 (disconnected weakly perfect simple graphs on n nodes). %Y A287009 Cf. A243252 (connected simple graphs whose fractional number equals its chromatic number). %K A287009 nonn,more %O A287009 1,3 %A A287009 _Eric W. Weisstein_, May 17 2017 %E A287009 a(9)-a(10) from _Eric W. Weisstein_, May 18 2017 %E A287009 a(11) added using tinygraph by _Falk Hüffner_, Aug 13 2017