OFFSET
1,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Graph Vertex.
Eric Weisstein's World of Mathematics, Graph Edge
FORMULA
a(n) = n*A000081(n).
G.f.: x * (d/dx) x * Product_{k>=1} 1/(1 - x^k)^(a(k)/k). - Ilya Gutkovskiy, May 26 2019
MAPLE
with(numtheory):
b:= proc(n) option remember; local d, j; `if`(n<2, n,
(add(add(d*b(d), d=divisors(j)) *b(n-j), j=1..n-1))/ (n-1))
end:
a:= n-> n*b(n):
seq(a(n), n=1..30); # Alois P. Heinz, May 16 2013
MATHEMATICA
b[n_] := b[n] = If[n<2, n, (Sum[Sum[d*b[d], {d, Divisors[j]}]*b[n-j], {j, 1, n-1}])/(n-1)]; a[n_] := n*b[n]; Table[a[n], {n, 1, 30}] (* Jean-François Alcover, Jan 25 2017, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved