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A137567
Number of chromatically nonunique simple graphs on n nodes.
2
0, 0, 0, 4, 18, 115, 905, 11642, 267398, 11821562
OFFSET
1,4
LINKS
Eric Weisstein's World of Mathematics, Chromatic Polynomial
Eric Weisstein's World of Mathematics, Chromatically Unique Graph
FORMULA
a(n) = A000088(n) - A137568(n).
PROG
(Sage)
def A137567(n):
d = {}
for g in graphs(n):
c = g.chromatic_polynomial()
d[c] = 1 if c not in d else d[c]+1
return sum(d.values()) - d.values().count(1) # D. S. McNeil, Jan 02 2011
CROSSREFS
Cf. A137568 (number of chromatically unique graphs).
Cf. A000088 (number of simple graphs).
Sequence in context: A052617 A141714 A220223 * A326261 A277473 A278994
KEYWORD
nonn,more,hard
AUTHOR
Eric W. Weisstein, Jan 26 2008
EXTENSIONS
a(9) from Eric W. Weisstein, Apr 07 2008
a(8) and a(9) corrected by Eric W. Weisstein, Jan 02 2011
a(10) from Eric W. Weisstein, Jun 09 2014
STATUS
approved