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!)
A323875 Number of labeled graphs on n nodes with two connected components. 3
0, 1, 3, 19, 230, 5098, 207536, 15891372, 2343580752, 675458276144, 383306076989440, 430041136692146912, 956431386434331323776, 4224539434553753578497024, 37106501188130085159785113344, 648740172906485727983524271405824, 22591360806791558877526051411343415296, 1567817808096346724727108606144936617617408 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

REFERENCES

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, 1973, section 1.2.

LINKS

Table of n, a(n) for n=1..18.

Marko Riedel et al., Proof of recurrence relation.

Marko Riedel, Maple implementation of memoized recurrence.

FORMULA

a(n) = A143543(n, 2).

E.g.f.: log(Sum_{q>=0} 2^binomial(q, 2)*z^q/q!)^2/2!.

CROSSREFS

Cf. A143543, A323876, A323877.

Sequence in context: A198046 A295812 A228229 * A001929 A349962 A230316

Adjacent sequences:  A323872 A323873 A323874 * A323876 A323877 A323878

KEYWORD

nonn

AUTHOR

Marko Riedel, Feb 05 2019

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 26 14:05 EDT 2022. Contains 354884 sequences. (Running on oeis4.)