A137568 Number of chromatically unique simple graphs on n nodes.

1, 2, 4, 7, 16, 41, 139, 704, 7270, 183606

Offset

1,2

Links

Table of n, a(n) for n=1..10.

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

Adjacent sequences: A137565 A137566 A137567 * A137569 A137570 A137571

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