

A007140


Number of unlabeled bicolored graphs, with no isolated nodes, on 2n nodes having n nodes of each color and allowing the color classes to be interchanged.
(Formerly M2980)


5



1, 1, 3, 14, 115, 2086, 101791, 14835870, 6852422567, 10338780759514, 51804974736769271, 872530598196790164797, 49930445153769776449253479, 9805619466642079028742952893709, 6670375074613812276139335045628924297, 15853216549413764390038207575938343994222273
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

0,3


REFERENCES

R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1976.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Table of n, a(n) for n=0..15.
F. Harary, L. March and R. W. Robinson, On enumerating certain design problems in terms of bicolored graphs with no isolates, Environment and Planning, B 5 (1978), 3143.
F. Harary, L. March and R. W. Robinson, On enumerating certain design problems in terms of bicolored graphs with no isolates, Environment and Planning B: Urban Analytics and City Science, 5 (1978), 3143. [Annotated scanned copy]


FORMULA

a(n) = (A054976(n) + A319155(n)) / 2.  Andrew Howroyd, Sep 25 2018


CROSSREFS

Row sums of A123547.
Cf. A007139, A054976, A319155.
Sequence in context: A180435 A256159 A122081 * A161936 A304983 A260887
Adjacent sequences: A007137 A007138 A007139 * A007141 A007142 A007143


KEYWORD

nonn


AUTHOR

N. J. A. Sloane


EXTENSIONS

a(11)a(15) from Andrew Howroyd, Sep 25 2018


STATUS

approved



