

A123549


Number of unlabeled connected bicolored graphs on 2n nodes which are invariant when the two color classes are interchanged.


2



1, 1, 2, 7, 36, 265, 3039, 56532, 1795771, 100752242, 10189358360, 1879720735880, 637617233537026, 400169631647375590, 467115844246503901102, 1018822456144128438039598, 4169121243929999956903622399, 32126195519194538601647462868271
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OFFSET

0,3


REFERENCES

R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1978.


LINKS

Table of n, a(n) for n=0..17.


FORMULA

a(n) = 2*A005142(2*n)  A318870(2*n).  Andrew Howroyd, Sep 04 2018


MATHEMATICA

A005142 = Import["https://oeis.org/A005142/b005142.txt", "Table"][[All, 2]];
A318870 = Import["https://oeis.org/A318870/b318870.txt", "Table"][[All, 2]];
a[n_] := 2*A005142[[2*n + 1]]  A318870[[2*n + 1]];
a /@ Range[0, 17] (* JeanFrançois Alcover, Sep 02 2019 *)


CROSSREFS

Row sums of A123550.
Cf. A005142, A318869, A318870.
Sequence in context: A259793 A112293 A090352 * A009704 A141308 A185161
Adjacent sequences: A123546 A123547 A123548 * A123550 A123551 A123552


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Nov 14 2006


EXTENSIONS

a(0)=1 prepended and terms a(8) and beyond from Andrew Howroyd, Sep 04 2018


STATUS

approved



