OFFSET
3,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 3..1000
FORMULA
G.f.: A(x) = ( B(x)^3 + 2*B(x^3) )/3 where B(x) is o.g.f. for A000081. - Geoffrey Critzer, Aug 09 2013
MATHEMATICA
nn = 20; 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]; b = Flatten[Table[a[n], {n, 1, nn}] /. sol]; CoefficientList[
Series[CycleIndex[CyclicGroup[3], s] /.
Table[s[i] -> Sum[b[[k]] x^(k*i), {k, 1, nn}], {i, 1, 3}], {x, 0,
nn}], x] (* Geoffrey Critzer, Aug 08 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved