A123549 Number of unlabeled connected bicolored graphs on 2n nodes which are invariant when the two color classes are interchanged.

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

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] (* Jean-François 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