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%I #28 Mar 14 2020 15:22:38
%S 0,0,0,4,18,115,905,11642,267398,11821562
%N Number of chromatically nonunique simple graphs on n nodes.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ChromaticPolynomial.html">Chromatic Polynomial</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ChromaticallyUniqueGraph.html">Chromatically Unique Graph</a>
%F a(n) = A000088(n) - A137568(n).
%o (Sage)
%o def A137567(n):
%o d = {}
%o for g in graphs(n):
%o c = g.chromatic_polynomial()
%o d[c] = 1 if c not in d else d[c]+1
%o return sum(d.values()) - d.values().count(1) # _D. S. McNeil_, Jan 02 2011
%Y Cf. A137568 (number of chromatically unique graphs).
%Y Cf. A000088 (number of simple graphs).
%K nonn,more,hard
%O 1,4
%A _Eric W. Weisstein_, Jan 26 2008
%E a(9) from _Eric W. Weisstein_, Apr 07 2008
%E a(8) and a(9) corrected by _Eric W. Weisstein_, Jan 02 2011
%E a(10) from _Eric W. Weisstein_, Jun 09 2014
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