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
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Sascha Kurz, Mar 25 2002
STATUS
approved