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

Author

N. J. A. Sloane, Nov 14 2006

Keywords

• nonn

References

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

Crossrefs

Row sums of A123550.

Cf. A005142, A318869, A318870.

Programs

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 *)

Formula

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

Extensions

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