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A079565 Number of unlabeled and connected graphs on n vertices which are either bipartite or co-bipartite. 0
1, 1, 2, 6, 16, 49, 129, 481, 1845, 9506, 57896, 463909, 4769436, 65179170, 1187099045, 29082860878, 960963147303, 42920936851975, 2594399793419459, 212465886865393053 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

G is bipartite iff the vertices can be partitioned into two sets such that all the edges in the graph go from one of these sets to the other. G is cobipartite iff the complement of G is bipartite.

For n >= 5, no graph can be both bipartite and co-bipartite. - Falk Hüffner, Jan 22 2016

LINKS

Table of n, a(n) for n=1..20.

FORMULA

For n >= 5, a(n) = A079571(n) + A005142(n). - Falk Hüffner, Jan 22 2016

EXAMPLE

Let G be a graph with 5 vertices, 4 of which form a path and the 5th adjacent only to the two vertices in the middle of the path. Then G is not bipartite nor cobipartite because there is a triangle in both G and its complement.

CROSSREFS

Sequence in context: A272411 A151528 A132803 * A052890 A052814 A192401

Adjacent sequences:  A079562 A079563 A079564 * A079566 A079567 A079568

KEYWORD

more,nonn

AUTHOR

Jim Nastos, Jan 24 2003

EXTENSIONS

More terms using formula by Falk Hüffner, Jan 22 2016

STATUS

approved

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Last modified December 5 13:38 EST 2016. Contains 278768 sequences.