OFFSET
1,6
LINKS
FORMULA
G.f.: Sum_{k>=1} k * x^(2*prime(k)) / (1 - x^prime(k)).
a(n) = 0 if n is prime, A066328(n) otherwise.
EXAMPLE
a(7) = a(prime(4)) = 0.
a(21) = a(3 * 7) = a(prime(2) * prime(4)) = 2 + 4 = 6.
MATHEMATICA
nmax = 90; CoefficientList[Series[Sum[k x^(2 Prime[k])/(1 - x^Prime[k]), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
a[n_] := If[PrimeQ[n], 0, Plus @@ (PrimePi[#[[1]]] & /@ FactorInteger[n])]; Table[a[n], {n, 90}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Apr 13 2021
STATUS
approved