A137567 Number of chromatically nonunique simple graphs on n nodes.

0, 0, 0, 4, 18, 115, 905, 11642, 267398, 11821562

Offset

1,4

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) - 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

Adjacent sequences: A137564 A137565 A137566 * A137568 A137569 A137570

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