login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A055542 Total number of nodes in all simple graphs of n nodes. 2
1, 4, 12, 44, 170, 936, 7308, 98768, 2472012, 120051680, 11208976504, 1981094071104, 656526407783376, 406758179201296832, 471397289547064631520, 1024016251272440926318848, 4180909690610059855623236192, 32176399052621010609861807435264 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..87

Eric Weisstein's World of Mathematics, Graph Vertex

MAPLE

b:= proc(n, i, l) `if`(n=0 or i=1, 1/n!*2^((p-> add(ceil((p[j]-1)/2)

      +add(igcd(p[k], p[j]), k=1..j-1), j=1..nops(p)))([l[], 1$n])),

       add(b(n-i*j, i-1, [l[], i$j])/j!/i^j, j=0..n/i))

    end:

a:= n-> n*b(n$2, []):

seq(a(n), n=1..20);  # Alois P. Heinz, Aug 14 2019

MATHEMATICA

Needs["Combinatorica`"];

Table[NumberOfGraphs[n]*n, {n, 1, 20}] (* Geoffrey Critzer, Oct 13 2012 *)

CROSSREFS

Equals A000088(n)*n.

Cf. A000169, A055543, A055544.

Sequence in context: A188632 A151460 A149364 * A149365 A000759 A076793

Adjacent sequences:  A055539 A055540 A055541 * A055543 A055544 A055545

KEYWORD

nonn,changed

AUTHOR

Eric W. Weisstein

EXTENSIONS

More terms from Sascha Kurz, Mar 25 2002

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 August 24 14:53 EDT 2019. Contains 326295 sequences. (Running on oeis4.)