|
|
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
|
|
|
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, []):
|
|
MATHEMATICA
|
Needs["Combinatorica`"];
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|