OFFSET
0,5
COMMENTS
An isolated vertex has degree 0 and a universal vertex has degree n-1.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 0..87
FORMULA
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-> `if`(n<2, 1-n, b(n$2, [])-2*b(n-1$2, [])):
seq(a(n), n=0..20); # Alois P. Heinz, Nov 06 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Nov 06 2023
STATUS
approved