

A004108


Number of nnode unlabeled connected graphs without endpoints.
(Formerly M2910)


20



1, 1, 0, 1, 3, 11, 61, 507, 7442, 197772, 9808209, 902884343, 153723152913, 48443147912137, 28363697921914475, 30996525982586676021, 63502034385272108655525, 244852545421597419740767106, 1783161611489937453151313949442
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OFFSET

0,5


COMMENTS

Also number of nnode unlabeled connected mating graphs, cf. A006024 and A092430 (conjectured by Vladeta Jovovic, proved by G. Kilibarda).  Vladeta Jovovic, Oct 07 2004


REFERENCES

F. Harary and E. Palmer, Graphical Enumeration, (1973), formula (8.7.11).
Goran Kilibarda, "Enumeration of unlabeled mating graphs", Belgrade, 2004, to be published.
R. W. Robinson, personal communication.
R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1977.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..50 (terms 1..26 from R. W. Robinson)
David Cook II, Nested colourings of graphs, arXiv preprint arXiv:1306.0140, 2013
Goran Kilibarda, Enumeration of Unlabeled Mating Graphs, Graphs and Combinatorics, Volume 23, Number 2 / April, 2007, pp. 183199.
R. W. Robinson, Connected graphs without endpoints  computer printout
Eric Weisstein's World of Mathematics, Connected Graph.


FORMULA

Inverse Euler transform of A004110.  Andrew Howroyd, Sep 09 2018


CROSSREFS

Cf. A059166 (nnode connected labeled graphs without endpoints), A059167 (nnode labeled graphs without endpoints), A004110 (Euler Transform, nnode unlabeled graphs without endpoints).
Cf. A092430 (nnode labeled connected mating graphs).
See also A261919.
Sequence in context: A185385 A024528 A273468 * A203007 A296321 A203768
Adjacent sequences: A004105 A004106 A004107 * A004109 A004110 A004111


KEYWORD

nonn


AUTHOR

N. J. A. Sloane


EXTENSIONS

a(0)=1 prepended by Andrew Howroyd, Sep 09 2018


STATUS

approved



