login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 19 06:18 EST 2022. Contains 350464 sequences. (Running on oeis4.)