OFFSET
1,2
FORMULA
L.g.f.: x * exp(Sum_{k>=1} ( Sum_{d|k} (-1)^(k/d+1)*a(d) ) * x^k/k).
a(n) = n * A004111(n).
MATHEMATICA
a[n_] := a[n] = SeriesCoefficient[x D[x Product[(1 + x^k)^(a[k]/k), {k, 1, n - 1}], x], {x, 0, n}]; Table[a[n], {n, 1, 33}]
a[n_] := a[n] = n SeriesCoefficient[x Exp[Sum[Sum[(-1)^(k/d + 1) a[d], {d, Divisors[k]}] x^k/k, {k, 1, n - 1}]], {x, 0, n}]; Table[a[n], {n, 1, 33}]
a[n_] := a[n] = Sum[a[n - k] Sum[(-1)^(k/d + 1) d a[d], {d, Divisors[k]}], {k, 1, n - 1}]/(n - 1); a[1] = 1; Table[n a[n], {n, 1, 33}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, May 26 2019
STATUS
approved