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 A137568 #30 Nov 29 2024 08:13:36
%S A137568 1,2,4,7,16,41,139,704,7270,183606
%N A137568 Number of chromatically unique simple graphs on n nodes.
%H A137568 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ChromaticPolynomial.html">Chromatic Polynomial</a>.
%H A137568 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ChromaticallyUniqueGraph.html">Chromatically Unique Graph</a>.
%H A137568 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SimpleGraph.html">Simple Graph</a>.
%F A137568 a(n) = A000088(n) - A137567(n).
%o A137568 (Sage)
%o A137568 def A137568(n):
%o A137568 d = {}
%o A137568 for g in graphs(n):
%o A137568 c = g.chromatic_polynomial()
%o A137568 d[c] = 1 if c not in d else d[c]+1
%o A137568 return d.values().count(1) # _D. S. McNeil_, Jan 02 2011
%Y A137568 Cf. A137567 (number of chromatically non-unique graphs).
%Y A137568 Cf. A000088 (number of simple graphs).
%K A137568 nonn,more,hard
%O A137568 1,2
%A A137568 _Eric W. Weisstein_, Jan 26 2008
%E A137568 a(9) from _Eric W. Weisstein_, Apr 07 2008
%E A137568 a(8) and a(9) corrected by _Eric W. Weisstein_, Jan 02 2011
%E A137568 a(10) from _Eric W. Weisstein_, Jun 09 2014