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A137568
Number of chromatically unique simple graphs on n nodes.
3
1, 2, 4, 7, 16, 41, 139, 704, 7270, 183606
OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Chromatic Polynomial
Eric Weisstein's World of Mathematics, Chromatically Unique Graph
FORMULA
a(n) = A000088(n) - A137567(n).
PROG
(Sage)
def A137568(n):
d = {}
for g in graphs(n):
c = g.chromatic_polynomial()
d[c] = 1 if c not in d else d[c]+1
return d.values().count(1) # D. S. McNeil, Jan 02 2011
CROSSREFS
Cf. A137567 (number of chromatically non-unique graphs).
Cf. A000088 (number of simple graphs).
Sequence in context: A192464 A360885 A343869 * A010355 A171880 A171874
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