OFFSET
0,3
COMMENTS
Invert transform of A007434.
FORMULA
a(0) = 1; a(n) = Sum_{k=1..n} A007434(k)*a(n-k).
MATHEMATICA
nmax = 28; CoefficientList[Series[1/(1 - Sum[MoebiusMu[k] x^k (1 + x^k)/(1 - x^k)^3, {k, 1, nmax}]), {x, 0, nmax}], x]
a[0] = 1; a[n_] := a[n] = Sum[Sum[MoebiusMu[k/d] d^2, {d, Divisors[k]}] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 28}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Mar 22 2019
STATUS
approved