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 A137567 #31 Nov 29 2024 08:15:32
%S A137567 0,0,0,4,18,115,905,11642,267398,11821562
%N A137567 Number of chromatically nonunique simple graphs on n nodes.
%H A137567 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ChromaticPolynomial.html">Chromatic Polynomial</a>.
%H A137567 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ChromaticallyUniqueGraph.html">Chromatically Unique Graph</a>.
%F A137567 a(n) = A000088(n) - A137568(n).
%o A137567 (Sage)
%o A137567 def A137567(n):
%o A137567 d = {}
%o A137567 for g in graphs(n):
%o A137567 c = g.chromatic_polynomial()
%o A137567 d[c] = 1 if c not in d else d[c]+1
%o A137567 return sum(d.values()) - d.values().count(1) # _D. S. McNeil_, Jan 02 2011
%Y A137567 Cf. A137568 (number of chromatically unique graphs).
%Y A137567 Cf. A000088 (number of simple graphs).
%K A137567 nonn,more,hard
%O A137567 1,4
%A A137567 _Eric W. Weisstein_, Jan 26 2008
%E A137567 a(9) from _Eric W. Weisstein_, Apr 07 2008
%E A137567 a(8) and a(9) corrected by _Eric W. Weisstein_, Jan 02 2011
%E A137567 a(10) from _Eric W. Weisstein_, Jun 09 2014