OFFSET
1,3
LINKS
Eric Weisstein's World of Mathematics, Graph Edge
FORMULA
a(n) = (n-1)*A000055(n). - Vladeta Jovovic, Jun 05 2004
O.g.f.: x^2 d/dx(A(x)-1)/x where A(x) is the o.g.f. for A000055. - Geoffrey Critzer, Jul 06 2020
MATHEMATICA
nn = 25; f[x_] := Sum[a[n] x^n, {n, 0, nn}]; sol = SolveAlways[0 == Series[
f[x] - x Product[1/(1 - x^i)^a[i], {i, 1, nn}], {x, 0, nn}], x];
r[x_] := Sum[a[n] x^n, {n, 0, nn}] /. sol; Drop[Level[CoefficientList[
Series[x^2 D[1/x (r[x] - 1/2 (r[x]^2 - r[x^2])), x], {x, 0, nn}],
x], {2}], 1] (* Geoffrey Critzer, Jul 06 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Jun 03 2004
STATUS
approved