

A005816


Number of 4valent labeled graphs with n nodes where multiple edges and loops are allowed.
(Formerly M3006)


2



1, 1, 3, 15, 138, 2021, 43581, 1295493, 50752145, 2533755933, 157055247261, 11836611005031, 1066129321651668, 113117849882149725, 13965580274228976213, 1985189312618723797371, 321932406123733248625851, 59079829666712346141491403, 12182062872168618012045410805
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OFFSET

0,3


COMMENTS

Each loop contributes 2 to the valency of its node.


REFERENCES

Goulden, I. P.; Jackson, D. M.; Reilly, J. W.; The Hammond series of a symmetric function and its application to $P$recursiveness. SIAM J. Algebraic Discrete Methods 4 (1983), no. 2, 179193.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Jason Kimberley, Table of n, a(n) for n=0..25
R. C. Read, The enumeration of locally restricted graphs (I), J. London Math. Soc. 34 (1959) 417436.


FORMULA

a(n) = N{E_n[S_4] * S_{2n}[S_2]}.


CROSSREFS

Cf. A005815.
Cf. A129429, A033301
Sequence in context: A267018 A262911 A163949 * A179470 A270524 A179471
Adjacent sequences: A005813 A005814 A005815 * A005817 A005818 A005819


KEYWORD

nonn


AUTHOR

Simon Plouffe


EXTENSIONS

Definition corrected by appending "where multiple edges and loops are allowed", reference to Read 1959, formula from Read 1959 (5.11), and new terms a(16), a(17), a(18) contributed by Jason Kimberley, Jan 22 2010


STATUS

approved



